Usually between 10-10.5 volts is the lower voltage limit. Keep in mind that you might have a small voltage drop between the battery and the heater based on length and wire size so the battery might read 11V but the heater will only see 10.5 (for example) so for best accuracy, measure the voltage at the heater and not at the battery. Generally they need to see a voltage drop below the cut off for 20 seconds before they cut out.Hey guys at what low voltage will the heater shut down usually?