When the battery becomes low, the red LED will flash and the HM100P emits 3 “DU” tones every 30 seconds. Please charge by using the USB charger or PC USB port. It normally takes about 2 hours to fully charge the battery. The LED will indicate red when charging and off when charging is complete.
Charging requirements: You can plug our supplied USB cable to your own USB chargers (wall charger/travel charger/car charger, etc.) with 5V/500mA-1A or PC USB port. It is OK to use most mobile phone chargers on the market.
Note: When you can’t turn off the Bluetooth interphone, you can turn it off as soon as you charge it