iPhone draining battery instead of charging

[weaponofchoice]

Ok, I have searched the forums for this issue but I have found none.

Sometimes, when connecting my iPhone 3g 16gb to my macbook pro, instead of charging the battery, it drains it. Not quickly or anything, but for example: it is 20% left, it charges 'till 70-80% it stays there, and then decreases until 20% again. I have to unplug the iPhone, restart it, and connect it again in order to charge.

Now, this issue is random, and it didn't happen until I upgraded to 3.0 firmware. And yes, the iPhone it's jailbroken (pwnage tool), and no, it's not unlocked.

Does anyone else have this issue? is this a common bug or something? Any recommendations on how to fix it (besides restoring the phone)?

Extra info: this only happens when connecting it to a computer, using the power socket it seems to work ok.

Thanks for the input, and sorry for the possible bad grammar and/or english.

 

[WickedRabbit]

Not sure if this is the cause of your issue, but if the laptop is off/power save mode then the USB ports from your Macbook may not be producing enough power to actually charge the phone. Instead, it will drain it because the USB power is keeping the phone active, but it's not pushing enough power to actually charge (i.e. it's power draining). I saw something similar to that in the iPhone help support. The same thing applies to powered USB hubs since they generally don't output enough power to charge anything larger than a bluetooth headset or mouse when the computer is off.