zlacker

No, I think it's fairly easy to see that a third of the charge suddenly disappearing is a fairly uncommon behavior.

Same for your Windows idea...

>>perchi+(OP)
"A third" is again fraction/percentage - it's still a representation stuff that depends on charge and charge cycles... and likely previous over charging and heat (Li-Ion doesn't like heat).

To put it simply: the charge level, usually, is just a lookup table for voltage (not under load).

>>xxs+I4
In case it was somehow magically unclear, it's not that I don't understand how batteries work, but that either that exact charge approximation mechanism is working exceptionally incorrectly, making it appear as if the battery suddenly lost so much charge, or the battery is a bust.

I do not know whether the battery is actually experiencing that sudden loss in charge, nor do I care, because in practice the end result is the same...