Re: Islander 36 electric inboard? diy
To pull 10kw at 12v, you need 620amps an hour. Assuming you want to use batteries for 2 hours, with lead acid batteries you would need 2400 amp hours of batteries (50% usable capacity), or roughly 24 normal sized deep cycle batteries at a cost or around $2,000 and a weight of about 1,440lbs. This is why battery powered propulsion engines are so rare.
It is doable if you are ok with very minimal run times, but 2-3 hours is of the far end of realistic. You also need to look at charging times. I haven't run the numbers, but my WAG would be 2-3 weeks with a 30amp charger.