The 7084VP+ (orange body) is the MISCO Glycol and Battery Tester. The battery for the light-source on this refractometer is contained in the ViewPoint Illuminator, a hinged coverplate, on the front of the refractometer. The ViewPoint Illuminator is completely sealed and cannot be opened. Although you cannot change the battery itself, you can purchase a replacement ViewPoint Illuminator. Just look for “ViewPoint” in the refractometer accessories category on this site. The replacement kit comes with complete instructions on how to replace the ViewPoint.