Our 3.7V standard sock battery delivers ample heat for hours on end via our Mobile Warming Technology. Now featuring Micro USB Charging. Fieldsheer uses only the highest quality Lithium-Ion batteries to ensure long-lasting power and battery life. These 3.7V batteries are compatible with only Fieldsheer Heated Socks. Features Our 3.7V standard sock battery delivers ample heat for hours on end via our Mobile Warming Technology. Micro USB Charging. Fieldsheer uses only the highest quality Lithium-Ion batteries to ensure long-lasting power and battery life. These 3.7V batteries are compatible with only Fieldsheer Heated Socks. Specifications Rating: 3.7V 2200 mAh Input: Micro USB 5V 0.8A LED Light Battery Meter Charge Time: 5-6 Hours Dimensions: 2.8in x 1.1in x 0.8in