Charge a three-cell nickel-based battery pack with a Li-Ion charger (2012) [pdf] (opens in new tab)

NiMH batteries are surprisingly robust.

I've long had Palm Pilot Vx which I bought 2001 and used daily till 2011 when I switched my phone to iPhone 4s. Then I did factory reset and put it back in box it was sold and shelved it. End of January this year I was thinking I need to start clearing up what I've saved and see if would recycle, sell or send something to a museum.

I put Vx charging on its docking thing and left it there overnight (first checking it was not getting any warm) and next day I picked it up to see if it still works. It does, battery status did show full. I fiddled it perhaps almost half an hour and battery status was still full. So I left it on desk and thought to check it daily how long does battery charge last if idle. I think it was fourth of fifth day when change was only perhaps 10% percent. I have no real recollection of how much standby idle days was left after that 10 years in use, it's too long back and I didn't take any notes of it then. Just wrote in note date when I put it back in box.

I'm genuinely surprised that 25 years old darn thing still works, when it had been 10 years in use and then 15 years shelved batteries completely drained.

Now that's something we've lost when moved Lithium batteries, which don't survive being years completely empty. NiMH's just don't care, they seem to sustain capability to charge and keep charge after long periods of time unused.

I've had few NiMH triple-A batteries in use 12 years and I thought that was a stretch, but no. That Vx blew my mind how robust device and it's battery are.

I was recently searching for NiMH charging ICs, turns out they basically don't exist. Most devices which charge their NiMH batteries implement low CC charging, which is slow. It's a shame, because NiMH batteries do have their advantages (safety, ease of finding replacements, etc.) and can be recharged fairly quickly if the charger is smart enough.

If it doesn’t overshoot it’s fine. Modern low self discharge (lsd) nimh’s like eneloops do not like to be held on indefinite trickle charge or be overshot. Older nimh were less picky about overcharge so long as current was below its reabsorption rate.

But really thinking about it, this method doesn’t match up with how I’ve experienced nimh behaving on a charge. Intuitively, I want to say this will cause some (reversible) loss of capacity due to not fully charging the cells. It probably works best on new-ish high quality cells, ones with a few full cycles on a good charger. negative delta charge detection won’t work here.

I thought this was about charging batteries made from coins. I'll stick do salt water lmao