Schumacher BAF-M2 Battery Monitor Plugs into a 12 volt automotive cigarette lighter receptacle Allows instant monitoring of battery and charging system voltage, alerting you once battery drops to 12 volts, giving you approximately one more hour of run time, depending on the system's wattage LED warning lights alert you when your battery or charging system is not functioning properly Detects problems with the alternator, diode and any variance of more than 0.8 volts Mounted display on your cars dashboard