The ThermaCELL Heated Insoles ProFLEX Battery Pack (HW20-XB) are extra batteries that is used for the Heated Insoles ProFLEX. It is great to use for all day outdoor activities and when traveling. It includes two rechargeable batteries that are made from lithium-ion polymer. It includes one wall charger, one smart charging case and one USB cable. The wall charger wires can be disconnected and can be used as carrying case for batteries instead. The batteries perfectly fit ThermaCELL Heated Insoles ProFLEX products, can be charged in 4 hours or less and can last up to 5 hours on medium setting and 3.5 hours on high setting.