Comment by MarkusWandel
8 hours ago
Am I courting disaster by reviving won't-charge pouch cells by just manually running a bit of current through them until they're nonzero volts and then a normal charger will do the rest? So far, in the maybe half dozen times I've tried it (rectangular battery blocks for old digital cameras, the pouch cell inside a long-disused Kobo Reader) it's worked. They charge right up, they don't swell, and they still have decent capacity.
I'm running at the hairy edge and only high quality safety engineering is protecting me here? Or these cells can take a lot more abuse than they're given credit for?
About 15 years ago I was writing software for an embedded device made by another company, and they sent us a unit for testing. It had a small rectangular rechargeable lithium battery that was charged via a DC jack.
At one point I hadn’t kept it charged, the battery went completely flat, and after that it would no longer charge at all. When I called the company, they said the battery was now too deeply discharged and required an “intelligent” charger to revive it. They sent a charger with a slot for the bare battery; some LEDs blinked in various patterns for a while, and eventually normal charging resumed.
I’ve always wondered what that charger actually did, that the built-in charger was not capable of. Was it performing some kind of analysis to decide whether the battery was safe to recover (e.g. after deep discharge), or was it simply applying some initial charge ignoring the battery’s protection circuitry (and at what risk)?
Over-discharged Li-ion cells can grow metallic lithium dendrites that result in internal short circuits. Charging them again following over-discharge does create a risk of fire/explosion.
I've thought before that it'd be nice to have some kind of device that would do this in a safe(r) fashion wherein you'd connect the 2 charging leads to the dead battery plus a temp sensor pad and it'd slowly bring the charge up to the minimum required for charging by a regular charger.
I've jump-started my share of batteries this way. Such a deep discharge might affect lifespan but it's typically old devices we do this to anyway.
Cool. I have a modern (not smart) body weight scale and it regularly ruins this way at least one of the 3 GP NiMh rechargable AAA batteries I put in it, so I wanted to hear some ideas what could be done with them given they have been through only bunch of charge cycles.
If it runs on 3 AAAs you could also hotwire it to use 1 lithium ion (choosing a model with builtin protection).