The parent unit has a rechargeable circuit and comes with 3 rechargeable batteries inside the unit so you can conveniently recharge it using the included micro USB cable. Use only these supplied rechargeable batteries for power supply. If non-rechargeable batteries are used, do not charge the parent unit under any circumstances. Should you wish to use a charger, use only a regular charger. It is strictly forbidden to use fast chargers to charge this device.