My battery says it was less than 5% when I turned it on so I plugged it in and 5 seconds later said it was around 77% charged. I do not believe that right lol.
Does the charge light between the USB and HDMI connectors go from red to green? If you have CWM installed you can try wiping the battery history and see if that helps. Otherwise your battery may be hosed.
While connected, go to market and download and install battery boost (I think that's the name. Its icon is a large green B). Unplug your tablet and allow the battery to completely drain. With the tablet off, connect the power until the red light turns green. Turn the tablet on and run battery boost. This fixed the battery problem on my Coby, hopefully it'll work on yours.