Designed for use with either the PROsine 2.5, or the PROsine 3.0 Inverter/Charger, or any TRUECHARGE 20 or TRUECHARGE 40+ Smart Battery Charger. This accessory gives the user added peace-of-mind by automatically adjusting the charger output according to the temperature of the battery electrolyte. This makes for a more accurate temperature-compensated charge.