Electronic USB Rechargeable Pocket Hand Warmer Portable Battery (LA360) This product is a mobile power & handy warmer which has Li-Batteries inside. This product is recharged by plugging them into the wall or a computers USB port. This is simple, safe and easy to use. will still up to 80% of standard capacities after 500 times charge Operation time :~10 hours (low),~7 hours (high);Surface temperature:(39c ~48c)