The battery pack for Hotronic’s insole heaters the Hotronic S4+ Battery offers enhanced reliability and longevity. The NiMH batteries have an increased capacity for a combined 30 % in higher average temperatures and longer durations on a single full charge, for better performance when you need it most: in the cold! And no matter where you go HOTRONIC’s advanced global recharging technology senses when the batteries are fully recharged and protects them from overcharging damage by switching to trickle current recharging