5510 problem with battery

[liteFun]

yesterday flashed mcu+ppm (which had several added ringtones) to my 5510. everything worked ok. battery was full.
then i listen those new ringtones. power off. "what the hell?!?!"
switched power on. battery indicates 3 bars. leave phone to desk and go smoke a cigarette.
come back and see that phone has power off. try 20 times power switch. then try charge. after 5 minutes try again to switch on.
then it works again. netmonitor test 20 says ~4.00V when charging.

i can't believe that my battery is so bad.
maybe i have done something wrong with mcu.
tonight i'm going to flash original mcu back.
i really hope that's software problem, not hardware.

[liteFun]

%#¤&!
charged whole night that battery. got flashed mcu, ppm & eeprom.
and then battery empty..

maybe it's time to get better battery than 950mAh blc-2.