I preheat my aircraft engine(s) when the ambient air temperature is below about 5degC. This is to reduce the demand on the starter, the battery, reduce the oil viscosity so that the oil pressure comes up quickly after start, to reduce friction due to different expansion coefficients between steel and aluminum, promote fuel evaporation, etc. i.e. I need to warm the entire mass of the engine which weighs >100kg.
It takes a 350Watt AC-line powered heater several hours to do that, so more than 3kWh of energy. An AA battery contains about 0.001kWh of energy...