MaxxDry GreenHeat Rechargeable Hand Warmer and Digital Device Charger, 4400mAh, Silver Temperature Setting: Low 107 Degree F & High 118 Degree F Multifunctional design also works as portable mobile phone charger. Standard use time: 4-5 hours Power Supply: Rechargeable (micro USB 5V/4400 mAh max input) Over Charge, Over Discharge, and Short Circuit Protections