I am replacing the batteries on my Formula this year and need some help. They are completely shot. Plus they are probably 6+ years old and no longer taking a charge. I have a SBC Stroker if this makes any difference. I do also have a battery switch installed.

My question is, I know I need a deep cycle for sure, but should I run two deeps cycles or one one deep cycle and a starting or one deep cycle and one of those dual purpose? I installed a new stereo this year so I know I will be pulling some power, but nothing ridiculous. One 600 watt max amp feeding two subs.

Also, while running the boat, do I put my switch in the all position in order to charge them both?

Thanks!

One to crank one to handle the house stuff. Go with deka if you can. Sold by batt plus or napa. They flat out last. And yes put on both to charge.

I agree, Deka is one of the best, but pricey. I have been running Interstates for many years. I change them out at 5 years, and they are still good.

Don't get the actual deka labeled ones. Get the ones from napa same batt 99 bucks (; all made by east Penn

Be careful of the very high CCA rated wet cell starting batteries. They are mechanically weak internally. I have broken at least two of them in rough water and I'm now sold on the glass matt batteries (AGM). They're tough as hell and last a long time in both applications.

One consideration is how difficult is your engine to start. A modern, stock EFI engine requires very little power from the starting battery and two dual purpose batteries might be just right.. Some old carburated antique might be different.

One dual purpose marine battery for starting and one deep cycle for the stereo.