There are several reasons why this could be happening. First, if your tablet is a bit older, it may be as simple as the fact that the battery is nearing the end of it's life. Secondly, you may just be running too many programs at once, which would have a negative effect on battery life. You could check out guide [[Audiovox T752 Troubleshooting#Section_Battery_Charging|HERE]] for more info on that.
A few other suggestions would be to lower the brightness of your screen or check for a battery saving app on the app store to help you out. Hope this helps!