This is something you will have to live with unless you opt for a different battery.

If you have the backlight set @ level 3 or 4, the batteries drain much faster. Set to 1 or 2 and you should see better performance.

If this continues to be a problem, consider replacing the battery with one with a bit more power. http://www.prontowizard.com or http://www.prontobattery.com