I know with 3D games, the battery on mine runs out after about 3 hours. Music lasts much, much longer, and videos are somewhere in between.
What I did was buy the Battery Doctor Pro app. It does the full cycle charge thing once the battery is under 20% ... But the BEST thing is that it gives you a detailed list of things you can do with however much battery life you have left. For instance, if I only have 30% power, it'll tell me I can read a Kindle book for 4 hours, play a game for 30 minutes, listen to music for 2 hours, etc. (Not exactly real stats there, but you get what I'm saying.)