I went with 2x of the 40ah lead acid batteries i will mark them 1 and 2 and only use them to move the boat
I bought 2x the 45ah lead acid batteries to run in parallel on the boat as a start battery
Its the cheapest i have found, 2 start batteries 90ah 380cca x 2 cost less than $60 total
2x trailer mover batteries cost less than $60 total
I couldnt buy half of a single marine battery for that cost