Thanks Rick. According to what I found on-line
Group 24 (G24): 10.25 L x 6.8125 W x 8.875 H, 70-85 Amp hours (AH)
Group 31 (G31): 13 L x 6.8125 W x 9.4375 H, 95-125 AH
Need a new battery tray for length. Batteries/tray sit on a fiberglass molded (G24) flat landing. Never look at how the trays are mounted but assume an extra 3" of tray plastic length is O'K.
Regardless of the battery's physical size, you will want a dedicated starting battery for #1, and a Deep Cycle battery for #2.
The construction of each is different, and is specific for it's use.
The cranking battery is designed for a short term heavy amp load, whereas the Deep Cycle is designed for lower but longer duration amp loads.
If your #2 bank is to be used for the HLBB (house load battery bank), Deep Cycles will serve you best.
I'm also assuming the cables and the battery tender can all be reused for a G31 AGM starter w/ Bluesea 7622 ML ACR.
The 7622 ML is a 500 amp ACR with ML (magnetic latch) capability.
It will serve as an ACR, and will also have the ability to allow you to select and use the #2 bank, but it will bring in the SLBB (start load batt bank) during engine cranking.
In other words, if you use the ML feature, you will want to use heavy battery cables for it.
Its a summer lake boat so I can get away with murder.
Explain please!