Built to keep you warm on the coldest days of the season, the Thermic S-Pack 700 B Sock Battery promises cozy toes with up to 8 hours of warmth. The most inexpensive battery Thermic has to offer, the S-Pack 700 B is thin and compact in profile - designed to fit perfectly with the heated Thermic PowerSocks. Outfitted with Bluetooth technology, the Thermic S-Pack 700 B Sock Battery can be controlled remotely through your smartphone using the Thermic Heat Control App. With the ability to adjust heat settings on each foot individually, these Bluetooth batteries offer the highest level of convenience both on and off the trail.