Mini Butterball 4Pcs 3.7V 18650 4000mah Protected Rechargeable Lithium Battery with 18650 Wireless Charger High energy density, long life battery. Provides excellent continuous power sources to your device. With overcharge / discharge protection function that you can use it without worry. This 18650 battery is compatible with various kind of flashlight and LED headlamps, bike lights, etc. Note: it is button top battery, will not suitable for some device which use flat top battery