Could doing this have ruined my Ipod?

So I didn't learn about the rules of the Ipod battery until like two weeks after I got the Ipod touch 4g and I feel like I ruined it a bit. I got my Ipod 11/18 and about 2-3 times I feel asleep from 12:00-2:00 until 7:20 with my Ipod display on playing games like bloons tower defense and having the screen display on. Also I sleep with a winter blanket and usually go under so it gets quite heated I would think. It seems to lose about 10% of battery from full when I play the scribblenauts for 10 minutes, is that bad? Also if I bring it into apple to check it how long would it take? Would I have to schedule?Could doing this have ruined my Ipod?
My brother has had 4 iPods now, and he always complains about the battery life going down dramatically when playing games, even if it isn't really that low. It may be that the iPod just can't measure how much battery juice is actually left whenever you play games, because that's the case for all of my friends with iPods and iPhones when they start playing games.