Hotronics Foot Warmer S4 Power Plus Custom Heating System Hotronics Sale! from $268.00 Qty. Add to Cart This item is currently on backorder but you can still purchase it now and we'll ship as soon as more become available. The Foot Warmer Power Plus CUSTOM comes with 2 Battery Packs, 1 Recharger, and 1 pair of Heating Elements with Cambrelle® Covers. For use in HOTRONIC‘s Heat Ready Insoles or on custom insoles, orthotics, or insoles of one‘s own choice. SKU: 1043 Tweet