Lithium battery that attaches with snap buttons to the top of the sock. Compatible with all Lenz heat socks, heat vest, heat bandage, heat glove 4.0 and LED System. The heat is adjusted in three levels via buttons on the battery or with the LenzHeat App for iPhone and Android, and lasts up to 14 hours. Specification: The battery pack is placed at the top of the sock, heat is regulated in three steps via the battery or the app. Battery life: Level 1 – 42 °C, 10–14 h; Level 2 – 52 °C, 5.5–7.5 h; Level 3 – 60 °C, 3.5–4.5 h. Includes global USB charger with display, 2 rechargeable lithium batteries RCB 1200 and 1 USB charging cable with indicator.