Electric defrost/heater ?

And a bad one. It takes a lot of current for a heater like that. Current= Amps. You are limited to 12+ volts so you will need a lot of amps. Most toaster ribbon bathroom heaters use 1200-1500 watts @110 volts. Think about it.
A 500w heater or amplifier should be the same thing to the electrical system ?
It will only be used now and then.