My battery drains faster on 6.1.3

I'm using and iPod touch 5 and I unjailbreak it and update at the same time. But when I update I come to realize that my battery drain faster on 6.1.3 .. When I charge my ipod full, I will usually play games like fifa or blitz

Brigade.. After I play those game for about 1/2 - 1 hour, my battery drained a lot.. Can anyone help?

I also wanna ask if my ipod is still under warranty after jailbreak.. But usually after jailbreak the warranty will be block or something right?

Sorry for my english