hey Bro, i got the same problem, i send the cell hpone to the seller and they said was a main card, that give the trouble, now i was watching in a russians page they change the LION Batery for a new one, and it works, i cant find one and then i just chance the cellphone for a new one, you can try with a Friend Batery
some one said to me was fake, but i try something, i charge the batery with and old Batery charger (with 2 Wires in the input, with 3A output (overloading obiusly isnt good idea for a long)) and put in on the cell phone and the G3 work good 4 a couple of days... then it die again... try that bro may be will work
PS: i change the software maybe 16 time, diferents download areas, and nothing work, for that i can tell you isnt the software