I am experiencing less than stellar battery life with my 720. The unit was purchased about a month ago, and although fully charged, I don't seem to get more than 1.5 to 2 hours of battery life before the unit shuts down. The advertised life of the battery is approx 4 to 5 hours and I am not close to getting that... Any tips on how to get more life out of this bugger without plugging it in??