What's the wattage on the dew heater?
If you have a deep cycle battery, it need be no more than 18a/h I'd say, but if the dew heater is a whopper, it'll be touch and go.
P= IxV - so you've got 18 x 12 = 216watts for an hour, or 113 watts for two hours or 56 watts for four hours
|