[SkunkBoat]

if its 5 years old its probably shot.

That battery at HD is really all you need and its a good price. But its bigger than a grp24 and you might have mounting space issues since you have 2 batteries.

I use a single grp 27 MDP (Marine dual purpose) and never have any problem starting and running electronics all day....until they get to 5 years, then one day you start noticing that the trim is slow when you first put it down, before the motor charges it. Thats the time to buy a new one.

since you have a starting battery, you can get a deep cycle at Wally World or AutoZone or wherever...except We$t Marine$$$
For the purpose of running electronics/pumps/lights, its the AH(Amp Hours) rating that is meaningful, not the CCA/MCA. The higher the AH, the longer it will run things.
IMO, unless you run an electric trolling motor, you don't need a purely deep cycle battery.