This Ryobi pack wouldn’t take a charge. After removing the “tamper proof” Torx screws I had my answer as to why: one cell had gone out of whack and fallen to 1.2 volts or so.
I tried boosting it up a little to see if it’d come back but the charger only ran for about a minute. I know, terrible idea, yada yada…
The protection/balancing board is neat. It’s got some kind of serial data connection on it (which doesn’t go to the tool, it’s for factory test/calibration) and two BIIIIG MOSFETs on a heatsink that I’ll be stealing for use in other adventures. But alas, this pack, it’s pining for the fjords.
Lithium ion batteries are kinda known to have a shelf life, so it’s not entirely unexpected that it’d go after a few years.