The new S4 Series are Hotronic's most powerful-yet-compact Battery Packs.
With enhanced reliability and longevity, the new S Series batteries maintain 55% of a full charge and 95% of their initial capacity after four years of non-use! Plus, an increase in capacity offers up to a combined 30% over the "e" and "m" series batteries on the same setting, all when needed most, in the cold!
If you currently have the older version of the Hotronic FootWarmers you'll want to take advantage of the longest battery performance and better charging by buying two new Power Plus S4 battery packs and the s/e/m series recharger. Use your current insoles with heat elements and save over the price of a new set of FootWarmers.