ESR644 is a modern high quality regulator that is a plug-In replacement for the OEM regulator on various Yamaha ATV models. We incorporated the newest version of our advanced power circuit and we combined that with our highly efficient heat sink. Our ESR644 offers superior performance compared to the OEM regulator. It combines very accurate control of output voltage with with the high efficiency of our rectifier bridge. The result is a perfect charge to the battery at any engine RPM and a much cooler running unit which translates into super reliability. ElectroSport offers ESR644 with a full one year warranty.