Originally Posted by knc1
Yup - battery problem.
The firmware only tests the "terminal voltage" of the battery - NOT the battery's capacity to store a charge.
For Li-Ion - the "aging effect" is to lose storage capacity - it will always re-charge to the full rated terminal voltage.
The portion of lithium in the battery that no longer takes a charge is referred to as its "rock content". That increases over time, even if stored new in the box. It increases faster with abuse, such as by discharging it too far (leaving it in diags mode, for example). It also increases as you use up its limited number of charge/discharge cycles, so for maximum lifespan you should only charge it when it shows a low battery (i.e. not every night).