The Lithium Pack rcB 1200 is a battery pack that works with all Lenz Heat Socks. The battery is rechargeable and can keep you warm for up to 6 hours, depending on both its temperature setting and the temperature outside. You can choose between three temperature settings that are adjusted directly on the battery or via an app on your smartphone. The pack contains 2 batteries and 1 charger. RCB stands for Remote Controlled Battery.