My battery has the 126.96.36.199 firmware upgrade. I hadn't flown for several weeks and as expected, today I found the battery partially auto-discharged (I had left it fully charged several weeks ago). Pressing the button would light up 3 LEDs. Plugged it into the charger to top it off, and nothing happened. The battery LEDs did not light up during the attempting charging. The light on the charger was lit, and I tried disconnecting and reconnecting the battery several times. Left it plugged in a few hours but still only 3 LEDs. Flew with this battery anyway and it was at 71% when I started the P2V up. I flew it until I got to 15%. Plugged it into the charger and now everything acted normally. LEDs light up progressively more during charging (as normal), and when finished the LEDs went out. Pressing the button lights up all 4 now. Is there some battery level threshold you must be below before the charging will begin?