Have you checked to ensure that the battery connector hasn't become loose or dislodged? Have you tried a hard reset of the iPhone by holding the power and home button for several seconds? Does the iPhone still charge when connected to a regular outlet?
It's in there pretty good and tight so you need to slide it up to release the screen, just don't be too rough with it as it's still delicate but it will come loose. You may need to work at it a little bit.