Yusko, the battery charge is not controlled by the firmware there is a tinychip on the battery that controls the charge process.
You could replace the battery they can be bought on ebay:
>> battery cell mp4 <<.
If you don't have a soldering iron to desolder the old battery and resolder the new you could also cut the old battery off leaving the wires and rejoin them to the new battery wires. Be sure to insulate the joins with insulating tape when finished.