Rechargeable batteries 18650 3.7V, pack type 2000mAh 4000mAh 6000mAh 8000mAh with protection circuit. Battery pack with charging circuit. Suitable for replacing equipment whose original batteries have deteriorated. or want to change to increase usage time longer Products that use this type of charcoal include: Solar cell lamp Headlamp or headlamp, Bluetooth speaker, etc. Voltage 3.7-4.2V Volts.