Im having the same problem, my phone works fine and is detected correctly when I connect it to the pc and when I try and use it on battery power the phone starts booting and when the carrier image appears the phone just vibrates and turns off. I can turn the phone on but only when I have it connected to the wall charger or the usb cable to the computer.
And if I pull the battery and connect the charger and place the battery again, it shows a battery charging indicator and wont load the OS. If I disconnect the charger and leave it a few seconds it starts loading the OS, while the OS is loading I connect the charger again and the OS starts up correctly with no problems.
The problem is that as soon as I disconnect the charger the phone turns off and gives the "Low battery, turning off handheld" message and the phone turns off.
I'm really frustrated with this problem and I don't want to get rid of this phone because it's really useful and I don't have money for a new one.
Any ideas anyone please???