Mobile Warming 3.7V Curved Bluetooth Premium Sock Battery Black. 7V 2200mAh Replacement Bluetooth Premium Sock Battery for Fieldsheer Mobile Warming Bluetooth socks. Specifications for Mobile Warming 3.7V Curved Bluetooth Premium Sock Battery: Manufacturer: Mobile Warming Color: Black Power: 3.7 volts Length: 5 in Additional Features: Lithium Battery Battery Type: Lithium Ion Package Contents: Mobile Warming 3.7V Curved Bluetooth Premium Sock Battery USB Charging Cord Mobile Warming MW37V22-N: 3.7V Curved Bluetooth Premium Sock Battery Black Mobile Warming MW37V22-N: 3.7V Curved Bluetooth Premium Sock Battery Black