The defunct 18650 lithium cell I used for the DSO150 power supplyprompted me to crack open a battery from a long-gone Dell laptop to see if any of its cells were in better condition:
Yup, gently crushing it in a vise splits the case enough to work the Designated Prydriver around the joint, a process considerably simplified by the knowledge the case isn’t going back together again.
Prying the top off reveals the cells and their connections:
One of the cells had corroded, accounting for the pack’s failure:
The others were undamaged, but had self-discharged down to about 1.5 V over the course of several years and refused to charge.
The moral may be to tear the pack apart as soon as it fails, a point always easier to recognize in retrospect.
So I taped the packs to prevent shorts and tossed them into the recycle box.
Most of the “dead” 1.5V or even lower cells will charge just fine if you jumpstart them with a bench power supply – the charger simply won’t even try when they are that low. Go slow, maybe 1/10C or less, limit the voltage to 4.2V and monitor temperature. When they get to 2.85V you can put them in a normal charger. You can dump any that jump straight to voltage limit as soon as you plug them in though.
I have many of these and they hold 1/2 to 2/3 of rated charge. “Healthy” ones that had over 3V when they were extracted usually hold something like 3/4 or 4/5 of the charge.
I won’t touch physically damaged cells or any with zero or negative voltage, and newer Chinese replacement packs – those are always crap. Rest are fair game, but they get monitored during charge cycle and I charge them in a middle of kitchen on a ceramic floor with nothing remotely flammable within 1m in any direction. Silicon fireproof pouches are also a good idea.
OK, I charged a pair of those cells (they were still welded together) from the bench supply set to 4.2 V and current-limited to 220 mA, with everything in the middle of the concrete basement floor. The voltage rose from 3 V, the current dropped to 40 mA, and the cells didn’t warm up at all.
However, when I clipped them into the battery tester and applied a 1 A load, the voltage immediately dropped to just about zero. Smaller loads had the same effect.
So, alas, they’re dead!