Help with espar heater drawing too much current

Hi

I have a D5 hydronic (installed on 36' sailboat with 2 deep cycle + 1 starter battery), that draws too much current, and gets F11 (unless shorepower connected or engine running)

I have a current meter installed. Shows 60-80 amp draw for first couple minutes. Also draws 50+ when heat cycle starts again.

Too much for my batteries, I guess. Since without shore power connection and inverter kicking in, it will not start

Suggestions?

Thanks in advance

70 amp draw x 12v is only 840 watts. Not much for a "space???" heater....not familiar with your application, but a lot for a battery to supply. A little bedroom electric heater for a house is usually at least 1700 watts. On shore power you have 10x the voltage so for the same heat you will only have 1/10 the current requirement. Makes sense that you could have problems on battery power.

An 800 AH battery will basically deliver 80 amps for 10 hrs. Figure on half that and it's an envelope of power, not 80 amps then nothing.

So the next obvious question is where did you inherit this problem. New to the boat, new problem, new heater?

Mark