HOTRONIC foot warmer E4 powerplus with heat ready insole Contents include 2 Battery packs with Integrated Heat Regulator, 1 pair of Heating Elements with Self Adhesive Fabric Covers and Strips, 1 recharger with North American and European plug adapters, operating instructions and limited warranty card Powered by high capacity, cold temperature operation, NiMH cells with 4 push-button controls its easy to adjust temperature-duration settings. Easy to read Battery Pack LEDs indicate setting selected and power on / off. Battery Packs m3 contain three 3 cells for powerful-yet compact design. NiMH cells do NOT have memory effect and do NOT require fully discharging before fully recharging.