If you have no way to charge them, I would pull them from the boat and charge them at home. Sitting around in a partially charged state is one of the main causes of premature battery death.
He is absolutely correct. The best battery service life results from recharging as soon as possible after any use - even if you didn't use them very much. The only sensible way to store a battery is fully charged. I would never use a storage facility that didn't have power for this reason.