Which is better? 2 Batteries Parallel or 1 Large Battery

[sonarandgps]

I recently purchased a boat and need advise on batteries. Troll motor I can use the 31 series and have space. But for starting battery and bilge, aerators, depthfinders I only have room for either Two 24 series(800CCA) or 1 large 31(1100CCA) battery. I am thinking if I run the 2 batteries parallel(connect N-N, P-P)that i would be better than running 1 large battery. I would put motor start on one battery and all other electricall on other. My motor is a Merc 175 optimax and they recommend 900-1000 CCA for start. Any opinions? thanks in advance.

[Lou r Pitcher]

It can work successfully ....buying at same time, discharging in parallel and charging in parallel.

My preference though with an engine that has dual charging outputs is still use two batteries but with one cranking the engine and the other running just the console. If something out on the water were to ever happen to one battery, a combine switch is installed and can be used for the good battery to emergency light a NAV light or crank start. Unsure, but don't think your Merc has Aux battery charging.

It would be a bit harder on your engine's voltage regulator's health to charge the two suggested parallel batteries if ever heavily discharged rather than just the one big one.

For your parallel batteries, best to wire your engine with one of its power leads on one parallel battery and the other power lead on the other parallel battery's opposite polarity terminal. Do same splitting with the charger's leads.

[STRETCH1]

Just get 1 battery. I use a Deka 27m6 which has 182rc and 1050mca for my starting battery. I got everything connected to the one battery and never an issue. I got a lot more electronics than you mentioned plus a 225 Opti. I got 3 HDS9s, 3D structure Scan, Sirius weather, nematode network, 2 power poles, Lights in every box, 2 biodegradable pumps, 1 pump out pump and 2 aereators