There are three set-able battery protection levels; "Hi" equates to 11.8 volts (High cut-out), "Ned" equates to 11.2 volts (Medium cut-out), "Lo" equates to 10.1 volts (Low cut-out). These are the voltages sensed at the refrigerator under load at which the compressor will shut down to protect your vehicle battery. If you have a small battery in a smaller vehicle, you should select high so that you are able to restart your vehicle easily. If you have a larger vehicle and larger battery capacity you should select the medium setting. If you have a dual battery set up and the secondary battery is able to be isolated from the starter battery you should select the Low setting.