Does anyone know how many amps a water heater circuit board and thermostat draws if there is no element connected. I plant to use a DC heating element connected to the battery using a relay. If the heating element isn't power through the AC power supply, how many amps would the other electronics probably use on a basic 20 gallon water heater without a digital display or anything like that. Would it be crazy to hook the AC to a light switch if the amperage is very low. That way the water heater can be turned on and off with the switch!