Hotronic Footwarmer S4 Universal 2 S4 Power Plus Battery Packs, with four cells and one 1 Recharger (back compatible with e and m series Battery Packs) 2 Heating Elements,1 pair of Cambrelle Covers and Strips, and 1 pair of Hotronics One Size Fits All  Heat Ready Insoles. Keep feet warm inside ski boots or easily transfer to other footwear Three base level settings for maintaining warmth, and a fourth setting offers an extra blast of heat The new S series batteries offer more than ever before, including enhanced reliability, longevity, and performance