Try this one on for size--I charged my jailbroken 5 overnight, as usual, and when I woke up it was at 100%, as usual. Browsed FB for about 35 mins on wifi, then went for a bike ride using Cyclemeter, which obviously uses GPS. I also had the iPod app running, but that was it, and the display was off the entire time. The ride lasted an hour and 20 minutes. Got home and had 20% showing, which almost immediately shot down to 12%. I rebooted and it went back up to 27% (which would still suck). Installed BatteryDoctorPro and connected it via USB to charge and it flew up to 50%. I've tried fully discharging and recharging and it's still wonky (which is a gross understatement for this behavior). I'm neither a n00b to iPhones nor jailbreaking (been doing it since my 1st iPhone, which was the 3GS), and have never seen anything this weird.