How long does the battery last and how do I know when it needs charging?

The battery run time is approximately 50 hours with an active Bluetooth link, and the stand-by time is 100 hours with no active Bluetooth link. When the battery is low and approximately one hour of use remains, an audio signal of 3 tones will sound in the headset. The headset will turn off automatically when the battery is fully drained. (Page 6)