Chuck,

It is not necessary to have a big heavy battery if all you want to do is
run to shore and back. Lawn tractor size batteries will do what you
want at a reasonable weight. If that is too heavy go with two small 6
volt batteries. I leave mine in the dingy and hook to a charging line
connected to my house batteries that keeps the dingy topped off and
ready to go. I find this much better than fooling around with a finicky
4 hp motor.

Ron