I'm running only stock ICS FF18 (guess I should stop waiting for my OTA FH13 update), but I had the same voltage issue with my E4GT. The battery wouldn't charge, no matter which cord I used (mine or any other). I took it to my local Sprint store that's the actual repair shop (where all the other Houston stores send damaged units), and they ordered me a new one. My best guess is that the micro USB charge port was somehow damaged, maybe from simple wear and tear. Wiggle the cord a little when it's plugged in...does the voltage error occur?