Batteries in parallel for reserve capacity

I am currently running 3 Humminbird Helix 9’s in my boat. Near the end of a big day of fishing i am loosing power to the units. My current battery set up is one starting battery and one house battery for electronics which is a few years old, Not linked together (One optima blue top(AGM for starting) and one conventional marine battery)
My question is….if I buy 2 new group 24 batteries with 120 min reserve capacity and hook them in parallel will ultimately double my reserve? As well with them being hooked together my Yamaha 115 should charge the batteries a bit while i am running around the lake?

Thanks Dave

When hooking 2 batteries in parallel, charging my be an issue, especially if you mix types (wet cell vs. agm). If you were going to buy something new anyway, will a grp 31 deep discharge battery fit into your spot.

A grp 31 deep cycle battery has an 195 min RC @ 25 amp draw, helix 9s draw 1 amp each. So doing the math one battery should be good for about 27 hours between charges.

An AGM and a wet cell deep cycle grp 31 battery have about the same RC specs. The AGM has a flatter discharge curve.

Hope this helps…Fish…On…

Yes, theoretically this should work, the problem is that you could possibly run into a situation where you drain your batteries and now you don’t have a primary starting battery to get you home. I think you might be better off with a single group 27 deep cycle to run your electronics and a separate dedicated starting battery. A group 27 battery has approx 100ah capactity and 3 Helix 9’s will pull about 3-4amps which should give you at least 20 hours of runtime. The other questions is if you are running a trolling motor and if so, how does that play into the equation?

Just thinking out loud but would one or more of the new lithium iron phosphate batteries work? They are spendy but might solve your problem. Would your starting battery run a small inverter that would be enough to plug a trickle charger in for your lithiums?

Two 30ah batteries that can be run in parallel with a 2.4 amp charger for about $350.
Or maybe I don’t know what the heck I’m talking about with this stuff!:???:
Lots of new battery technology.

Amped Outdoor Batteries

Thanks for the comments. I recently was able to turn my optima starting battery sideways and push to the back of the compartment. This allowed me to get a new house battery with 210 min RC in the compartment. This is an additional 50% more RC than I had before. I believe I should be set from here on out.

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