Ask HN: What are you working on (August 2024)?

I thought the reason the packs are sealed is to stop amateurs from swapping in cells of differing voltages, which short each other out and cause sparking/fire hazards. There's a reason li-ion battery charging is current-limited, they have no internal resistance.

from their homepage :

A Fireproof Casing which REALLY Works!

Scared of battery fires? I know that we are!

This is why our Infinite Battery comes with a casing that we designed to resist the heat of a fire, thanks to it's thick aluminum casing, and a design which dissipates heat quickly.

And YES THIS WORKS! We have put a massive effort in making our casing sustain the battery fire, and extensively tested it (videos coming soon), so you can sleep safely (and us too!!). See our complete fireproof testing on our documentation/FAQ

Prevention is better than cure though. plus you've got to consider cell gassing/venting/explosion risk/toxic fumes as well as fire prevention.

If they were doing per-cell protection, fair enough (cheap 18650's don't have cell protection usually), but I think they are still connecting 4 cells in parallel, with only serial-bank MOSFET's like in usual sealed packs.

(if they're using PTC themistors between the parallel cells to prevent over-current, it's all good though I suppose)

As I understand it, it's somewhat the opposite for internal resistance. You need to have current limiting in place because the internal resistance of the cell is turning that current into heat, and heat is the enemy of batteries.

(Probably there's also a complicated chemical reason for current limiting that I don't fully grasp)

>and extensively tested it

By themselves or independent 3rd parties with deep experience in battery safety testing?

Also spot welded connections work well, transfer reasonable amounts of current and don't tend to vibrate off during use. We tear down packs at my job and there are warnings inside some not to re-use cells for vapes, they really don't want you taking these apart. Larger packs like EVs and E-bikes are probably worth refurbishing and repairing.

> a casing that we designed to resist the heat of a fire, thanks to it's thick aluminum casing, and a design which dissipates heat quickly

Thus turning a difficult to deal with Li-Ion inferno into a slightly less difficult to deal with block of superheated aluminum, that will happily set on fire anything that looks at it funny?

This is always my concern about fire-proof metal casings for batteries: where do you put that so it doesn't set anything on fire?

Indeed, we recommend swapping all the cells at once! But using our battery it means that you recover cells in perfect conditions that you can use in second life applications!

Indeed it will get hot, but it is better than having one's house burn down! :)