guys I have the same problem, I did all the things, even replaced 2 times usb flex cable, but still have voltage problem, slow charging (it takes up to 10 hours to fully recharge, and drains fast), and it powers up automatically if I restart, shutdown, or reinsert battery on the phone. Also I replaced battery & wall charger, but still the problem occurs. The technician cannot find other defects after replacing two times new usb flex cable. Now I got the phone back and still with problems. Any idea what could be the problem? Thank you.
btw; im using cyanogenmod 10 nightly (jelly bean), i'm 100% sure that its not software issue, tried everything like flashing custom roms (went from original ICS), still it doesn't charge fast and shows over-voltage. Its ******* annoying.