To see how much battery charge is left, you can press both volume buttons at the same time for an LED indication of your battery level.
Hold down both volume buttons to activate the indicator. Release to stop the indicator.
Approx. 0-40% Battery Charge
Quick red flashes from the LED, and a quick beeping sound
Approx 40-100% Battery Charge
Slow white flashes from the LED indicator, and a slow beeping sound