Fieldsheer Men's Premium 2.0 Merino Heated Socks - new Premium 2.0 Heated Socks are powered by our Powersheer Micro BT 3.7-Volt Lithium-Ion battery that provides long-lasting warmth for up to 10 hours on a single charge. Calf Length L/R Design Comfort toe Heavy cushioning in key areas Arch Support Heal and toe reinforcement No slip features Heat under toes Comfort Contour Bluetooth Battery Up to 10 hours of heat Battery Features: Powersheer Mini B Rechargeable Lithium-Ion Comfort Contour Battery (3.7V 2200mAh) Up to 11 Hours of Power Per Charge UL/CE certified Bluetooth enabled Battery size: 8in x 1.8in x 0.5in USB Charge Cable included Charge Time 3-4 hours* *Charge time is based off using a USB-A wall charger that delivers 5V@2.1A Style: FSMPREM2