Flytouch 3, Do you have problems with it?

[AllyKat]

Okay, To start off, I got a Flytouch 3 for Christmas. I charged it for how much a note said inside it (3 hours). I then took it off and started messing around with the background and stuff, but the battery started to get low in within 15 minutes. In within 30 minutes, it was down to 56%. I left it on, and charged it for 30 minutes. It was off when I tried to check to see what percentage it was charged. Every time I try to charge it, It turns off. When I leave it alone for 30 minutes, it turns off. When I want it to sleep, and I come back to it in 5 minutes, I press the power button at the top(if you are holding it sideways where the square is to the right) and it sorta messes up. It turns gray with lines on it for a split second then shows the unlocking screen. It also lags from time to time.

Can anyone tell me how to improve the battery life and not make it lag and freeze up?

I NEED HELP! A S A P