Replacing batteries on a 228

[fathergoose]

I recently purchased a 2009 228G with a very good electronics package. It includes VHF, Raymarine ES128 with 4KW radar and a 4' open array and a Fusion stereo. I had difficulty with the batteries at the end of last season so I am replacing them. I'm pretty sure that they are the original batteries. My question is should I replace them with larger capacity batteries? I bottom and drift fish a lot with the motor off and the fishfinder and stereo on. I typically have radar on when I'm running. Due to the space available for the batteries I can not go to a physically larger battery.
Thanks and sorry for the excessive detail but I wanted to provide as information as possible.

 

[Doc Stressor]

You are pretty much limited to Group 27 batteries because of the space constraints. You might be able to squeeze in Group 31s, but you would only get an extra ~10% capacity for your trouble.

Gradys typically come with Deka 27M6 batteries that are very good dual purpose units. They are flooded cell, but are maintenance free, so you hardly ever need to get to them to add water. I've had really good luck with these in several boats. Figure on a 5-7 year service life.

You could go with a true deep cycle for your house battery. You gain a bit of capacity but lose cranking amperage if you need to use the battery in an emergency. You will need to use a battery isolator/ACR or the Yamaha Auxiliary charge cable to keep your starting battery isolated from the deep cycle house battery. It's good to keep multiple batteries separated even if they are identical.

Depth finders pull very little current. I leave mine running all day with the engine off. But some sound systems draw a lot. Check the current draw of your particular Fusion setup. You may need to go with a third battery in the cabin if you run the system all day when at anchor.

 

[SmokyMtnGrady]

Group 27 as Doc says. You could all out and do AGMs but it's not necessary. I doubt they are OEM batteries. With that said what ever you do, don't connect them in parallel by connecting the negative terminal of battery 1 to the positive terminal in battery 2. Trust me I know said outcome.