The Lenz Lithium pack RCB 1200 fits all models of Lenz heat socks, lenz heat vest and heat bandage 1.0. The battery attatches to the legband of the sock via press studs and then folds over to secure in place. The heat can be regulated with 3 different setting on the pack or changed to suit yourself via Bluetooth on your smartphone. This battery pack will give you 14 hours of heat, more than enough for a day on the mountain. Match me with the Lenz Heat sock.