I've got an iphone 3g with a strange issue, it won't boot off the battery or from the USB cable attached the computer - but when I connect it to the mains it boots to the connect to iTunes screen no problem - as soon as I pull the cable from the mains charge it cuts out. I thought it might be the battery, so I swapped the mobo out of the case into another housing with what I know is a good battery inside - but it hasn't made a difference. I have checked the contacts on the Mobo are clean, and also the connections are fitting well - so the only other thing I can think of is it is a battery manager issue on the Mobo? Or is there something I have missed that could be causing this?