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

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.

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.

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.

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.

>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.

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.

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.

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.

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.

> 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.