The power on/off button has a light on it that changes color from green to yellow and flashes red when battery is about to be depleted. It turns yellow when plugged in and charging and green fully charged. It's my practice to keep it plugged in unless there is no power available so I know it's fully charged when I need battery power. I always recharge ASAP after using it on battery. This type of battery doesn't develop a memory like the old ni-cads. The specs say only 4 hours at full power but it is usually longer depending on the music source.