Another thought if you have a cooperative marina. Use a fork lift to lift the batteries up to the boat. Once at deck level it will be relatively easy to bring the batteries on board.
Last fall we used the yards front loader to take the life raft off the boat. The operator brought the bucket up under the LR and I released the straps. It dropped right in, and down it went in the bucket.
Last fall we used the yards front loader to take the life raft off the boat. The operator brought the bucket up under the LR and I released the straps. It dropped right in, and down it went in the bucket.