Originally Posted by gavin
Remember car batteries arnt sealed,... this is why we often top up with de ionised water...
Lots, if not most, car batteries are now spill proof and sealed so as never to need topping up. They have a wee vent which can take a tube. This can be vented directly out of the battery compartment/console so that no hydrogen gets trapped inside the boat.
I've a small one sitting at the side of me. 270CCA and 33A/hr, cost £22. 48A/hr is probably more than adequate for your engine.