Im running 2 group 31 blue top optimas for my 80 Fortrex on my PIV and they are holding up great and last all day. I run the biggest Sears Platinum for my starting battery, it runs my livewells, a Lowrance HDS10, HDS7 and 2 Structure Scan units with no issues. If you get Optimas, buy the biggest ones (31 series). Mike