I'm no stranger to Li-Ion behaviour, having studied them a fair bit and having designed commercial chargers. I think I know what the issue is here, but would appreciate informed comment from others.
Laptop pack, "Li-Ion 10v8 @ 4500mAh" Haven't opened it up yet, but NiXX chemistry wouldn't achieve the capacity in that size anyway.
Charge in laptop (AC on, machine off), indicator LED goes green after ~ 3 hours. After 1/2 hour "rest", boot to Windoze on battery power, on-screen gauge shows 100% declining to 54% after 2 hours operation. Resume AC supply, turn machine off, battery recharges to green LED status (not timed). Rest 1/2 hour, measure pack terminal volts =12v51. Leave pack out of machine.
Ten hours later, measure 12v48. Alles ist gut. Insert pack into machine (no AC) and boot. Reach desktop, then machine shuts off. Restore AC, reboot and check on-screen gauge - "2% and charging".
Clealry the pack has usable capacity as it sustained 2 hours' operation without drama. Clearly the pack did *not* self-discharge in the ten hours. Right now it is "recharging", meaning going through the motions to satisfy the electronics - while the pack is already effectively at full SOC.
What I failed to do is measure the pack voltage *after* the premature shutdown. Will do that on a later test.
Possibilities that I see are:
(a) the pack protection module decided prematurely (on some basis) that the pack was exhausted.
(b) the laptop, based on data (or lack of) from the pack's electronics, made that call. The pack is "brand X", and the on-screen SOC panel tags it "standard APM battery" and "Manufacturer: unknown"
Anyone seen this type of behaviour before? Comments? Ideas?