Toyota is recycling old EV batteries to help power Mazda's production line

had to check: toyota owns 5% of mazda which makes them the largest shareholder.

TIL as well

Neat idea to mix batteries of different age and chemistries. I've wondered why EVs couldn't do that too with some power electronics and SW. If an EV battery could have multiple such modules, it'd:

1) Make it easier to carry a cheaper lighter less-natural-resources-consuming battery most of the time. Go to some "gas station" to rent and add more modules when taking a road trip

2) Make it cheaper to replace the 1 module used a lot at its EOL, thereby making EVs last longer and be viable as cheap used cars even past 10 years like ICE cars are

3) Allow easier upgrades as chemistry improves: solid-state, sodium ion, etc.

Modules could be electrically tested for fit. I'd think the fit range would be quite wide (e.g. if one supported lower max discharge rates than another) given the headroom we have with EVs' power these days: they have far-more-than-needed power (which mostly comes for free with EV range).

The tradeoff is that they'd need to be built to be modular with some standardization on module dimensions (maybe we'll have "ZZ" size like we have AA, C, etc today), and would take a tad more volume in the vehicle (though the limiting factor is weight rather than volume). Easily worthwhile over the current model with a huge monolithic pack.

This seems very bizarre given Mazda is probably the least (of all "major" manufacturers) focused on EV and electric initiatives.

Mazda only had one EV, the MX-30 EV. Less than 600 of the MX-30 EV were sold in the US during its production. It was a complete flop right out of production. Mazda leadership has been notorious for pushing rotary engines and shifting further away from EV initiatives.

Did you even read the article? It has nothing to do with producing EVs, they are using the old EV batteries to help power manufacturing facilities.

I have to imagine that even accounting for the variance in internal resistance over a large set of batteries in a demanding application like a car is probably a host of problems makes this unattractive from the outset.

This is very bizarre because that's exactly what GP was pointing out.

it's unrelated to the manufacturing of EVs. If any factory reaches a significant energy generation (usually this means from solar) it makes sense to look into a battery solution. It just happens to be Mazda's manufacturing plant.

IIRC; Toyota started investing in Mazda to gain access to their engine technology.

https://en.wikipedia.org/wiki/Skyactiv

https://thedetroitbureau.com/2019/07/toyota-teaming-up-with-...

It's quite likely that lower discharge rate requirements are a large part of what makes this system function. Batteries with different internal resistance can work reasonably well even in a naive series system at low discharge rates but absolutely will not work at high discharge rates.

I suppose this has a better chance to happen in city trucks than in cars. Delivery trucks are used more heavily, owners care more about efficiency, they are bigger and taller, so they can offer easier structural options to house swappable batteries. Also, swappable batteries could make charging very fast, if a sufficient stock of batteries is kept on a charging station.

Cars could follow, but it's significantly more involved in them. In most cases, the batteries are a relatively thin layer covering the entire floor space, or similar.

Technically a bank is a much larger shareholder (https://www.mazda.com/en/investors/stockinfo/situation/), but Mazda and Toyota have been collaborating for a long time with joint manufacturing (https://en.wikipedia.org/wiki/Mazda_Toyota_Manufacturing_USA) and technology sharing. Toyota has similar arrangements with other companies like Subaru and Suzuki.

Re: 1, ignoring the complexities, is really interesting but depending on the effort to change our battery banks quickly makes renting a car more feasible.

And this highlights American traffic and sparseness.

- plug-in hybrids have 10-13 mile range which is great for running a few errands (this is only slightly more feasible than in a golf cart or ebikes) - also great for last mile connectivity for mass transit n users;

- the Nissan leaf 2012 had an 80 mile range - perfect for most daily commutes in a metro area

- modern electric vehicles have 200-300+ mile range, good for weekend getaways; esp with a charge at the destination

Mazda as a company has a very good track record of adopting green production initiatives. For example, they were one of the first to switch to water based paint to reduce VOC emissions, and specifically formulating the paint to not require heat-drying to lower energy use.

Their current stance seems to be that PHEVs are better than EVs for the environment because it better matches the driving patterns of the typical customer and charging availability, and minimizes the weight of the vehicle and production of batteries, both of which are still contribute significantly to pollution.

Toyota also owns Daihatsu, which is a lesser known name in the US, but is a major maker of kei cars, which are huge in Japan and other parts of Asia.

They also own Denso, which is the second largest auto parts company.

And they partner with Subaru on some things, such as the Subaru BRZ and Toyota GR86, which are basically the same car with different badging.

In theory, that seems sound. In practice, there is very little information on efficiency details for vehicles like the CX-90 PHEV. At first glance, it seems other manufacturers are outperforming Mazda's PHEVs with standard hybrids.

There are so many questions this (the battery storage) raises regarding ROI and alternatives. I think it's great they're trying something, but I can't help but wonder if this will be another failed attempt on their track record.

The batteries are sourced from manufactured EVs. This is a later stage of the battery lifecycle that began with manufacturing of an EV.

That's a trust account though, they're just holding shares on behalf of fund managers or individuals. They also generally don't vote.

So for all intents and purposes, Toyota is the largest singular voting shareholder.

seemed like they were pointing out that Mazda EV offerings are bad and that they don't worry about EV initiatives. That doesn't have much to do with studying how to put older batteries to use - EVs can be bad for many reasons.

To me it seems perfectly reasonable to try to find a way to leverage depleted EV batteries for a factory - whether or not it's producing EVs or not.

exactly.

state-of-charge / depth-of-discharge vs lifetime accumulated "discharge stress" so to say also matters a lot.

batteries aren't simple, even lifepo4 ones.

GM claims that this is exactly how their Ultium battery pack architecture works. It is made up of multiple modules each with their own BMS, and supposedly one module can be replaced without having to be a match in chemistry and degradation to the other modules.

I'm unsure if that will actually work so well in practice, where you still need to charge all the cells simultaneously when doing DC fast charging etc.

Also all of that extra architecture adds cost and complexity to each vehicle that rolls out the door, compared to a pack that just packs in a bunch of cells together with the necessary cooling etc. as one contiguous unit.

Given that EV battery packs in the real world are trending to last longer than the cars they come in, going with a simpler pack design and swapping in a refurbished pack if you experience a premature failure might be the more economical route.

Toyota owns a de facto controlling stake in Subaru (~20%).

Due to typical Japanese corporation by-laws, it only takes 33% share ownership for uncontested control of a corporation, and >50% of 33% means they'll never lose a vote for simple majority matters, which is basically everything except selling or dissolving the company.

The 20% threshold is for a guaranteed seat on the board, which lets them put issues up for a vote.

I hadn’t thought about different sizes/weights but this does remind me of Nio’s battery swap network. Which I’ve always been fond of in principle. I think at some point in the future, when range isn’t such a competitive advantage in the EV space we’ll see a push towards standardization and something like this will likely occur. I’d guess something around the 1000 mile mark for an EV. Absurd, yes, but at that point no one will complain about range and that sort of implied density/efficiency also allows for a better towing experience (at least here in the states). If someone can get a 1000 miles of range, but only drives 100 miles at a time TCO drops immensely because tires/brakes last much longer at lower weights.

TIL Mazda isn't a wholly owned subsidiary of Toyota. I thought it was, now I wonder where I got that from.

actually if you can get a late-1990-ish 90-100cc 2T japanese scooter like Honda Lead 90 or Suzuki Address 100, or even later Yamaha Neos / MBK Ovetto 100cc of 2005-ish vintage this whole discussion about ranges and fuel consumptions becomes pointless.

because those have had fuel consumption of like 2-3L per 100km. with fuel tanks of about 6L you had all the range for errands you could possibly need.

and they were capable of moving two persons around _and_ moving a ton of grocery, or something like an ironing board.

hell, in 2000s we were doing 700km trips on them.

PHEVs were quoting 20+ miles on electric last decade, I think 25-35 is common now?

Actual distance depends on elevation changes and speed/driving, but 15-20 is quite acheivable, as long as you don't make it to highway speeds. And if you go a bit farther and use a splash of gas, no big deal, that's why it has a tank.

Those who TL;DRd - it's for the factory, not the cars!

Old EV batteries are great for energy storage. A worse weight-to-capacity ratio doesn't matter for batteries sitting on the ground. A battery that holds only 70% of its original capacity is considered worn-out for EVs (and even replaced under warranty), but grid storage isn't driving anywhere, so any capacity left is still useful.

At the cell level they don’t degrade linearly. First it’s slow then it’s fast and then it’s abrupt collapse. You probably have noticed that yourself with old devices. Some do not hold charge even for a minute.

With battery packs probably you can do some smart things to make the degradation curve look more linear, but again there is only so much you can do.

Small 2-stroke engines tend to be worse for pollution emissions (NOx, particulates) despite generally good fuel efficiency.

Sudden failure in a big battery like these is usually due to a single cell failing, which can usually be replaced and then the battery pack is back to the 70% capacity or whatever. Probably in this context of scale it's worth doing the work of replacing bad cells.

CATL announced a dual-power battery pack recently.

https://technode.com/2025/04/22/catl-says-its-next-gen-dual-...

well, yes, I like the smell of 2T exhaust in the morning.

still, even my yamaha majesty 250 of 1992 (4HC-edit) only ate 3.5L/100km despite hauling thrice the mass of that same ovetto.

If you’re ever in Hiroshima I can recommend a trip to the Mazda museum (Cosmo! 787B!), which includes a factory visit across a raised gantry. It’s free, but you need to book in advance: https://www.mazda.com/en/experience/museum/

I saw that 787B at the Adelaide motorsport festival, MAN that thing makes an incredible noise!!!

There’s quite a lot you can do when you can isolate and deactivate individual cells, big battery packs like this really do not fall off a cliff in the same way you’re describing.

this is like picking up unfinished cigarette butts and making few finals puffs before burning your mouth.

worn-out batteries can swell and fail spectacularly, with fireworks

Also an iconic paint job. Mazda UK did a special edition MX-5 with a turbo and that paint to celebrate the Le Mans win: https://www.pistonheads.com/news/ph-features-heroes/ph-heroe...

> Due to typical Japanese corporation by-laws, it only takes 33% share ownership for uncontested control of a corporation

It doesn’t make any sense.

Ownership changes over time. At one time ford was in control. Which is why I checked - what toyota is doing makes no sense until you see current situations, now there is an obvious expected return on investment (if it works out of course- if it does they will do this to their own factories, if not they will write it off and not lose much.)

If you take car EV batteries and use them for stationary storage when past end-of-life, the fire risk becomes fairly substantial because EV batteries often have a little water ingress, physical damage etc.

It can be solved by isolating each battery in its own steel box, but that gets fairly expensive fairly fast.

You do realize these batteries you're referring to resale at a decent price because, for the most part, they still function really well, just not in its existing capacity.

How do you achieve this with cells in series? Do you kill an entire row and put it on "maintenance voltage"? I know how balance charging RC batteries work but they're smaller scale and "single row".

Also in RC car world it's generally preferred to have one cell per voltage step, I've had way more dual-cell(per series) packs fail than single ones. Though my experience is only 6s/~22v but it's "the same shit on a bigger scale" as far as I can comprehend.

re: Subaru

Perhaps more relevant, the Subaru Solterra and Toyota bZ4X (renamed bZ for 2026) are on a shared EV platform.

Maybe they can also make the boxes out of concrete for a lot cheaper?

How much distance does one pack realistically need to not cascade? Honestly I can't imagine any more than half a meter since air is an extremely good insulator. Just make sure the fire can't crawl across though cable insulation?

I've personally set RC lipo on fire with the wood-nail-hammer technique and while the fire out of the pack is intense I can't imagine it igniting another pack.

Battery banks are worse than degraded raid arrays in some important respects. The bad cells tend to try to bring the rest of the pack with them. It’s one of the reasons people keep toying with partitioning cells and putting controllers onto individual cells or small groups of them.

Parting out two or three dead battery packs to cull the best of the survivors can improve things quite a bit. And as you say, on a stationary pack you can afford to overdo telemetry, cooling, and safety circuitry because it doesn’t have to move, let alone accelerate.

I don’t know what the half life is like for the reused cells though. Do the cells that lasted twice as long as their neighbors continue to outperform or do they revert to the mean over time? I could see either being true. The days when you accidentally produce cells that are several stddev better than your target quality should make cells that last longer, unless they’re sold to a leadfootted driver.

No EV that I'm aware of has the ability to bypass a single cell in a series string.

I have often wondered if it would be worth designing an EV battery that can permanently short out a bad cell in a string, perhaps by deliberately disabling balancing, letting the bad cells voltage fall to zero, and then perhaps having a single use 'bypass' that latches on.

It wouldn't be a seamless user experience, because if you discharge the cell to say 0.5 volts but then the user tries to charge their car, you can't let them, since you cannot safely charge a lithium cell which has fallen below the minimum voltage, but you also cannot bypass it till the voltage falls to zero. Could be done automatically at 3am though like system updates.

Precautionary principle. There’s not good ways to extinguish these fires once they start. So you kinda have to let them go. Maybe you could use some sort of deluge system or aggressive liquid cooling on the surrounding cells however. Overbuilding the delivery system but then running the pumps at their most efficient cfm except when the smoke alarms go off.

Car power packs are batteries in the other sense of the word. They can be disassembled and culled. So what matters is the health of the best 1/kth cells in the array not the overall array health.

I guess you can put a relais/switch in for each cell in a series but then you need to account for voltage differences when taking them out. Either by over provisioning within the series and rotating in different cells. Or by have other strings take up the slack.

Either way you need some form of overbooking / compensating capacity.

I believe we have a new generation of supercapacitors in R&D stage. There were some experiments done in the last year that showed that some assumptions about what makes supercaps work so well turned out to be wrong. I can’t recall the details but it turns out the foamy structure of charcoal is not the optimal structure. So that should result in higher energy density per unit volume.

Think of it like how Zuckerberg only owns 13% of Facebook but has >60% of the voting power.

Japanese law allows corporations to only require 1/3 of voting shares present for quorum, and then a majority of those present to pass resolutions. It also allows cross-shareholders (like Toyota) to have special privileges over regular class shareholders (typically right of first refusal over any resolution).

In practice, nothing much will pass without the largest shareholder's approval.

I think you may be confusing worn-out batteries with damaged batteries, these two subclasses do not have the same properties

You shouldn’t need to charge them all at the same rate. Put in some cells that charge slower, fast charge the rest and continue charging the slower cells until unplugged. Consider for instance fast charging the array to 70% instead of 80%, where 1/3 of the cells are charged to 50% and the rest to 80%.

Related: Ford once had a 33.4% stake in Mazda and there was a bunch of cross-pollination between the two companies at that time. My 2002 Mazda Protege was loaded with various parts bearing the FoMoCo logo. And Mazda engines/chassis powered a bunch of Ford cars world-wide.

I’ve done the math a couple of times and IIRC if we can get the charge density per kilo to about twice what lithium ion can do, you hit a point where a deposit battery that’s around 20 kilos has enough range extension to start being worth doing. That’s the weight of a large bag of kitty litter or a commercial bag or rice. Put a good ergo handle on it and most people should be able to lift a few of them consecutively.

But until one unit is worth about 8 miles of extended range, there would be no point. 3@25 or 30 miles might make it worth the trouble for a road trip, or camping.

More often than not these bad cells can be removed, manufactured a new, and reinstalled. Not 100% but almost good as new.

Making your own cells is fun.

For Toyota, this is trivial and the energy storage these “left over” batteries provide, given a tinkering, is sufficient.

They also owned a chunk of Mitsubishi Aeroplane and IIRC invested in Mitsubishi’s 787 manufacturing division.

Your own cells? Like you put together a lasagna of metal sheets and chemical goops and roll it up?

Clarification, that announcement is for a new version and they're already selling packs with mixed battery chemistries.

Nearly all EV's today would run just fine on 3.7 volts fewer.

My car's high voltage circuitry seems to work down to about half of the nominal voltage.

Nah, you can buy 18650 cells, nickel strips, a spot welder, and make a BMS. Build your own battery pack.

Of course you do. As long as someone else pays for cleaning up after you. There have always been leeches in the world.

When all of your cells are connected in a pack of 400-800V connected to a DC fast charger, how do you stop charging the fast cells and continue charging the slower cells?

I've seen a video on the youtube where a battery recycling company does this; they leave the car battery packs in their original housing, which I presume is water resistant enough. Each unit is also connected to a controller, which I also presume monitors battery health, temperature (assuming temp sensors on car battery packs), voltage, etc. If a unit is dying they can safely dispose of it, else, the units were out in the open and with several meters in between, meaning any fire would be unlikely to spread to something else and there's plenty of access opportunities.

Very space inefficient though, but there's more than enough of that in the US.

Mazda punches way above their weight when it comes to "moonshot" innovation over and over again. Few of them really "succeed" commercially (Rotary engine, miller-cycle engine, HCCI) but I respect them for constantly pushing the technology forward.

* https://en.wikipedia.org/wiki/Mazda_Wankel_engine

* https://en.wikipedia.org/wiki/Miller_cycle

* https://en.wikipedia.org/wiki/Skyactiv#Skyactiv-X

* https://en.wikipedia.org/wiki/Homogeneous_charge_compression...

Except that the cigarrette is only 30% smoked and still perfectly fine to smoke for a while longer (if you insist on an analogy).

Car battery packs are really good; even the oldest Teslas are only now getting to less than 80% capacity. They are designed not to swell/fail if they're worn, else there would be a lot more car fires.

your comment reminds me of a rant by a severely clueless person who insisted that we must conserve water despite living on an island in a middle of a second largest european reservoir.

which is utterly pointless.

25-35 is common, and some like the Prius PHEV can do 45.

A relay would allow you to switch it out and then back in again. Which you don't need. Just a fusible link that can be blown to permanently disconnect the battery from the string might be simpler and more ideal for the application.

Eh, the math is probably pretty different with massive quantities of packs in racks.

I’m imaging every firefighter I’ve ever known suddenly having the hair stand up on the back of their necks.

Separate power factor circuits for each pack, I would think. With everything switching over to GaN now and bringing the prices down that should be doable.

How would they prevent two owners from owning 35% each? Could owner A vote something on Tuesday, and owner B vote something different on Wednesday?

A degraded battery bank does not mean a bank with outright "bad" cells. The cells will probably be way more off than they used to be, but there can still be plenty of effective capacity in the bank. Heck, if space isn't an issue, it's productive as long as it isn't self-discharging too fast.

You can still have a working battery even with some "bad" (i.e., way out of spec) cells, depending on the BMS. All the thresholds are configurable, just that a regular EV setup would lean towards safety.

In theory, yes, if those shareholders each keep not attending the meeting called by the other shareholder, they could both independently pass or undo each other's actions.

In practice in a hostile situation, they'll be courting the remaining shareholders to gain majority and won't miss those meetings, which tend to also have rules about how quickly or often they can be called.

It is also legal and typical for the bylaws to include poison pill provisions that would automatically protect the existing >33% shareholder, preventing a second >33% shareholder from existing (thus requiring multiple smaller existing shareholders to join forces to overthrow the largest shareholder).

plus if you aren't making your packs unrepairable on purpose with foamed construction (like Tesla). you can par out modules in the packs into new configurations somewhat easily for the amount of work needed.

If you don't know what you're doing, don't do this. Even if you know, probably don't. It works, and is a regular industrial process, sure, but you're trying to perform controlled melting of the protective housing of one of the many, tightly packed chemical energy bombs you're sticking together. Doesn't take too much of a mistake to go very wrong.

If you're building a battery pack in this day and age, use something like LiFePo prismatic cells and bolt-on busbars instead - way less dangerous chemistry, way less spicy process - but realistically speaking just buy the premade packs. For normal sizes, they're not more expensive (but don't buy the "too good to be true" ones) and means not having to deal with entirely unprotected battery terminals eager to give you a Very Bad Time.

There's usually a pretty big gap in time between 'worn' at say 70-80% of original capacity, and a pack that has actual failed cells in it too.

What's interesting is that if the batteries are being sourced from JDM cars the batteries are probably relatively young due to the average age of Japanese cars being relatively low (8.7 years) and the amount of yearly mileage is also half for JDM cars when compared to the US. So if you tried the same in the US it may not be as viable.

It's almost like EV batteries don't last long...

Generally speaking the cells that are welded on are designed to be welded on in the areas were you do the welding. Doing something other then welding on them properly is going to be more unsafe then welding.

The proper tools to do this are not that expensive anymore in the greater scheme of things. It is just a question of whether or not it is worth to do it at the scale you are doing it or pay somebody else to do it.

Of course if you buy cells that are designed to be bolted together then bolt them together.

Of course the bolts, or whatever else provides the threads, on those cells are welded on.

that is remarkably different from building your own CELLS. You are building your own pack in whatever series and parallel configuration you want. Which i agree is fun and a good skill

A few tradeoffs you might not be considering:

EV battery packs operate at voltages that are seriously hazardous. Consumers coming anywhere near those plugs is a non-starter, so even more bulk, weight, and complexity would need to be added to make the installation process foolproof.

Waterproofing is critical, the mechanism has to work flawlessly over insertion/removal cycles to keep a watertight seal.

Turns out they're lasting much longer than expected: https://news.stanford.edu/stories/2024/12/existing-ev-batter...

Great points. Re safety, I wasn't imagining the consumer doing it themselves but some robot like ones imagined for whole-battery swapping (e.g. https://youtu.be/Oj6LaYFall4); I think any battery swapping only makes sense for batteries you rent rather than own.

Is the failure mode of whatever chemistry is in an EV that they just conduct electricity? Li-Po usually fail in more spectacular ways than so.

> Generally speaking the cells that are welded on are designed to be welded on in the areas were you do the welding.

... by automated spot welder programmed to the specified timing and temperature control from the cell spec sheet, in a controlled environment with suitable protection and fire suppression for a battery manufacturing line. Not by a hobbyist's first try with a homemade spot welder and a safety squint.

I have made such spot welder and done such spot welding. Sure it's fun to do stupid things, but it remains stupid and unnecessary. For a homebrew battery bank, this is the wrong tool, wrong cell and wrong chemistry.

Buy premade, or if you must, buy boltable prismatic lifepo cells. They can dump a lot of power if your short them, but you can drill straight through them and they'll remain stable. The random 18650 li-ion cells... Not so much.

Of course it does. When you apply zero thought to anything you can always find false equivalence.

Do we use the precautionary principle when we run nuclear, build dams and burn coal as well or is this an extra thing because it's a potentially good way to reuse EV batteries? I don't think we should build these hand-me-down EV batteries near population centers, but my understanding is that the worst case scenario would be the plant burning down and releasing bad things (hello coal & natgas) into the atmosphere?

If we could develop some basic standards for packs (which voltage steps per row and some kind of connector interface standard like for charging) I think we have a really good way to maximize the lifetime and use of EV batteries to help the environment.

I paraphrase Bill Gates: There's no one energy source which will save us, many will complement eachother.

>The bad cells tend to try to bring the rest of the pack with them.

This is true (and in some cases potentially dangerous) when you have a several cells of varying voltages in parallel but it's fairly trivial (by EE standards at least) to overcome this with something similar to a charge pump.

Nope. Why would Toyota even have an abundance of "old" EV batteries to begin with if they "lasted much longer than expected".

I have a Toyota Landcruiser from 1990.

Which most likely wouldn't pass Japanese vehicle inspection performed, IIRC, every two years. Also this means that it was never totalled.

Plenty of cars suffer the latter and with safety systems as they are now, it's more likely than in the past.

I would expect you could only do it with the onboard charger and only if it has one charger per module or the ability to connect the singular charger to each module.

"Do we use the precautionary principle when we run nuclear, build dams and burn coal as well" ayfkm?

Why can you not bypass until the voltage falls to zero? I'm with you aside from that.

You are talking about cells going bad and they are talking about cells that have less capacity from being cycled, not the same thing at all.

Toyota sourced these from many places, not just their own vehicles...

BYD Seal DM-i has a plug in range of 125km / 78mi.

Username checks out. :D

I don't really know or care what any of this is meant to mean, but you can't comment like this on HN, regardless of the topic. We have to ban accounts that do it repeatedly.

https://news.ycombinator.com/newsguidelines.html

We detached this comment from https://news.ycombinator.com/item?id=45043113 and marked it off topic.

A great range extender weighing twenty kilos is available right now, a diesel generator.

It can also double as a air/water heater, emergency power for household or medical appliances, and emits about as much carbon in 30 years as it takes to manufacture a battery pack.

Context: there are chopstick shaped, ultra cheap, Chinese battery tab welders as well as no-brand battery tab value-packs to use with, available online.

One tabs each are placed onto each ends of cells, held down with the sticks, and instantly welded upon push of a button. This is much safer than heating up the whole battery by attempting to solder wires directly onto the battery cells(which are made of unsolderable materials anyway). The tabs limit heat conduction into the battery and it is considered safe to solder onto them.

If you're going to build your own battery pack no matter whatever whoever says or do, this types of cigarettes contain significantly less amounts of nicotine and tar components than others.

Looks like this is a PoC for Toyota's "sweep storage system" using "low voltage MOS", which seem to be a fancy invented term for a charge/discharge current limiter. [2] has photos of previous PoC from 2023.

1: https://global.toyota/jp/newsroom/corporate/43207750.html

2: https://www.power-academy.jp/sp/electronics/report/rep03200....

Don't forget about radiant heat! There's a pretty much perfect insulator between the sun and Earth conduction-wise, yet it is still pretty cozy up here.

Honestly surprised Honda hasn’t designed a hybrid that’s more generator and less hybrid but I suspect that has to do with air and noise pollution loopholes for generators versus engines.

No I’m talking about what warrants putting a pack on the secondary market and they’re being unreasonable. Just being 80% of initial capacity isn’t going to prompt someone to swap the batteries out. A damaged pack will.

I don’t know to be honest, I just know that you can find second hand car batteries that have been used for 15/20 years that still have 40% charge and I don’t know of any single phone battery that’d be the same. I could be talking out of my ass but that’s what I thought.

That’s so cool

There's NCA (drones), NMC (laptops, phones, many electric cars), LFP (stationary/grid), and LFMP (many new electric cars; slightly more expensive but higher current variant of LFP).

Seconding that advice to just use prismatic lifepo cells. Those have become really cheap, too: You can order brandnew 1kWh cells for $60ish + shipping even if you only need single digit quantities (those want to be squished a bit for longevity, so you might have to design a suitable enclosure).

Energy autarky has never been so affordable, progress on batteries and solar panels was awesome over the last decade.

> Very space inefficient though, but there's more than enough of that in the US.

Well, you could perhaps put photovoltaic cells on top to use that space? Your battery park needs to be connected to the grid anyway.

> There’s not good ways to extinguish these fires once they start.

If one battery pack catches fire, you can start moving the others away from it.

If you normally keep 0.5m between them, you have plenty of buffer space to eat into.

Basically it would start as . . . X . . . with X being the pack on fire "." being a battery pack not on fire, and " " being the half metre between them. Then you move them to get:

... X ...

Where the dots now have perhaps only 30cm between them, but the space to the X is increased.

Dams bust, nuclear blows up. It's rare but it happens. Their worst case scenarios are worse than a park of batteries burning down on a gravel/concrete park?

Your interpretation seems to be "we don't use caution when building them" which is not what I meant at all, we do but the risk is non-zero.

That's fair, I don't know how to calculate this but my naive assumption is a burning pack won't radiate enough to combust something 1 meter away if there's circulating air around.

What does "imagined" mean? Nio has been doing automatic battery swaps on a mass scale for years.

Balancing multiple battery packs at different wear levels is a huge nightmare. You have to run rebalancing operations all the time and on used packs it can be quite dangerous to trigger a thermal runaway.

If they do it with different types of batteries it is even more complicated, like you need to write some custom software to sync all that up. This is not a trivial project.

Also, you lose the ability to mold your battery along the bottom of the car, using dead space and keeping the center of gravity low. Gas tanks aren't even boxes, they are molded to fit around other parts with no dead space. So, add that space efficiency loss to all the additional space needed for access panels, installation foolproofing, additional waterproofing, etc.

So? They considered it to be worth while for them. Thus are working on it.

It feels like Neo is the opposite of where things should go. The great thing about EV is that every outlet is a refueling station. More EV charging for apartment buildings and parking lots feels like the answer. Those battery swap stations are insanely complex and expensive, and the complexity and added weight on the car are very significant. Unlike a gas station that just needs two nozzle types, or an EV charging port standard, having to standardize battery packs for everything from compacts to trucks would be a nightmare. Most people are not taking hundreds of mile road trips most of the time. Slow charging your car while it sits at home or at work or at the shop will work for 90% of cases. I could see the case for industrial or work vehicles, where keeping them running constantly is a legitimate need, but for personal vehicles that sit in driveways, parking lots, or garages 80% of every day, battery swaps feel like massive overkill.

I know, it seems it is fairly large operation however, if it wasn't I would assume it was a PR stunt.

This is definitely not worth doing for small scale operations. As far as I know there is no generic solution for doing this kind of thing (I used to work in the area, but not directly on the BMS systems).

If you just close the bypass switch, a large current will flow out of the (dying) cell, making a lot of heat.

You could have a two-way bypass, disconnecting the original cell, but that would cost more. Remember the bypass switch is duplicated for every series cell group (hundreds) and must carry the whole battery current.

Or you could have some kind of slow drain resistor - but then you're back to the time issue.

> How do you achieve this with cells in series?

You don't, if one cell fail you shut off the whole array of cells that is in series. But a pack has several arrays of cells.

Nobody is out there opening packs and replacing single cells, a battery pack is usually composed of multiple modules and each module can have multiple arrays of cells in series. You shutoff the whole array of cells around the cell that failed and the battery keeps working fine at reduced capacity.

If it happens multiple times in the same module you replace a whole module of cells. The packs can usually be disassembled and parts replaced, but the modules are usually soldered down to prevent/mitigate thermal runaway.

Also you can't mix cells of different chemistry or capacity together in the same module. So really if one fails in a module you replace the whole module. Or, in their case, just keep the module there disconnected until the whole battery fails then you scrap the whole battery pack. I assume it is not worth it for them to do any kind of replacements.

There are lots of car battery packs out there on the secondary market for many different reasons. Not every single battery pack is taken out from a good car because it has a bad cell.

they’re being unreasonable

No one is being 'unreasonable' you just started talking about something different.

Cars get scrapped for many reasons and might not have anything to do with the battery pack. I don't know if you have ever heard of junkyards, but people have been going to them for years to get perfectly good parts from junked or totaled cars. The average age of Japanese vehicles is only 9 years old. Most people don't drive cars to 150,000 miles and beyond. If Toyota is using the batteries from older cars, that by definition means they were still useful batteries on those cars.

I really don't know what to say about your 1990 vehicle comment. Good for you? Just because some people own a classic car doesn't change the fact that more than 99% of classic cars are scrap metal now.

Ehhh it really depends. There are plenty of vehicles that are getting traded in where manufacturers/dealers would rather just replace the batteries.

I'd wager the bulk of them are hybrids where the batteries see a pretty aggressive charge/discharge cycle on a relatively small capacity (and therefore being relatively cheap to replace compared to a full electric). Of course then there are also full electrics where the owners get upgraded capacity or replacements due to degradation from use.

And importantly they aren't just recycling EV batteries here. They are using lithium-ion, nickel metal-hydride, and lead-acid batteries. So they are also buying up traditional ICE automotive batteries as well.

Also worth noting this project is a collaboration between Toyota, JERA, and local universities for use at JERA's facilities. JERA is a large battery reprocessing and recycling company so they are already getting second hand batteries into their facilities on a regular basis. This project is primarily about doing the design and engineering work necessary so that JERA can set up an array of these battery containers, get notified when a unit fails, and swap out the battery with one from their stock for recycling.

Nah, the BMW i3 had one of these as an option, as does some Chinese car, with no regulatory difficulties. Also a common arrangement for ‘hybrid’ buses and trains.

They reuse inverters too. So the packs are separated, no need to balance.

> precautionary principle when we run nuclear, build dams

Yes. Dams in particular. You calculate for various failure modes and you design around mitigating the disaster if failure should occur. That's why dams are designed with emergency spillways. If there is a bunch of rain, gate failures, etc and you suddenly have more water than you know what to do with, you have the emergency spillway as a last resort. They exist to route water in high volume out of the resevoir, often in a sacrificial manner in an attempt to prevent the dam from failing. And if a dam would fail, it's preferably that it do so at the emergency spillway than elsewhere. So there is a certain amount of "in certain conditions failure can/will happen so this is how we design the system to fail as gracefully/least destructively as possible".

Nuclear has this as well. The plans for this are called "Severe Accident Mitigation Guidelines" or SAMGs with the general practice being called SAM (same abbreviation, just drop the G). Each nuclear site has them and they are generally framed as "this shouldn't go wrong but if it does". You can try to avoid those failure modes but they can always still potentially occur and the most you can do is just try to keep the damage from spreading to the best of your ability.

I think the "low voltage MOS switch" is just a roundabout way of saying MOSFET, which is very common in power electronics generally.

Okay, I understand. I was definitely imagining some sort of latching switch, that would connect to the bypass instead of the cell. Makes sense that would be more expensive.

This is not recycling. Recycling implies that you can produce the same product again many times; it's a sustainable practice. This is repurposing or upcycling. It's cool they're getting a second life, but they won't get a 3rd, 4th, Nth life unless the batteries are actually recycled into their component materials at end-of-life. It's kind of like the plastic brick companies: cool that plastic is being turned into a construction material, but it doesn't mean we can stop mining for the primary source material any time soon.

> It’s one of the reasons people keep toying with partitioning cells and putting controllers onto individual cells or small groups of them.

I have been out of the battery tech game for a while now but decades ago we were balancing individual NiCd and NiMH cells for optimal performance, is this basically the same thing?

https://electronics.stackexchange.com/questions/463591/nicke...

Usually a group of cells are welded together using a conductor. If they are in series, you need to balance the cells using balance leads. If they are in parallel though, they are balanced ahead of time to prevent too much current between the cells and thereafter they will balance themselves once they are wired in parallel.

In a parallel bank, a single cell going bad can bring down the rest to the same voltage. Even worse, if the bank is directly connected to other banks it can take out them as well. Also, if there is an internal short in one battery, the rest will pump current through it very effectively lighting it on fire. Individual battery protection circuits, smart switches, and internal short detection can help with this.

Yes, this happens sometimes.

Search this page for "PTC": https://www.electricbike.com/inside-18650-cell/

The PTC protects the rest of the battery if a single cell internally fails short.

The i3 certainly had some us regulatory difficulties, they had to change the battery and fuel tank sizes.