Don't know if you will ever want to use the grid heater system but it does draw down your battery and dim your headlights while it's drawing about 120 amps (I measured this). I drive along in the winter for the first 3-5 minutes looking like I'm flashing my lights at on-coming vehicles. If you live in a cold weather climate and run the glow grid you may think about two batteries but only if the dimming headlights bother you. The pre-glow period on a grid heater will not keep your starter from turning over the engine and firing. I would suggest going with a high capacity battery if only one is used with the glow grid heaters.