I use VLC Player when I'm unplugged and playing movies.
OneAnswer is right: if you have AC power available, use it, especially when doing more power-demaning tasks, such as playing video.
Run on battery whenever you need to and plug it in whenever you can. You can plug or unplug any time you need to, regardless of the charged percentage, and you never need to completely drain your battery.
The link below should answer most, if not all, of your battery/charging questions, including tips for maximizing battery performance. If you haven’t already done so, I highly recommend you take the time to read it.