The ActionHeat 3V batteries are super slim, sleek, and powerful. They are designed specifically for ActionHeat socks. They fit perfectly into the battery pocket on the top of the socks.Specifications:Lithium-Polymer CoreBattery Voltage: 3-Volt/1 amp output maxCharging Time: 3-4+ hoursBattery Care:It is important to maintain at least 25% of your battery power when not in use. Failure to do so may result in performance problems and reduced battery lifeDisconnect the battery packs from the socks when not in useDo not wash batteriesCompatible with:ActionHeat 3.7V Wool Heated SocksActionHeat 3.7V Cotton Heated SocksActionHeat AA Wool Heated SocksActionHeat AA Cotton Heated SocksSock Battery Set Includes:(2) 3.7V 2200maH Rechargeable Batteries(1) Charger Wire