Advice on a not so great battery setup

[Derek in AZ]

Howdy,

I have a 98 Maxum 3200 SCR. Twin 7.4L V8 w/ bravo III. Before I purchased it in 2011 someone really worked over the electrical system. In a nutshell, the only way that anything works, is to run both selectors on Both. Yeah... i know, not so great, risky, should have it rewired... but... im not gonna do that. I have always ran both banks each with two 6V GC batteries. However, the batteries I purchased last time seemed to have less CCAs than the previous bunch. The current set is on its way out and I am going to purchase new ones. Should I just stick with the 4 6V batteries? Or should I put some sort of High CCA battery on one side to get the current for cranking and keep 6V on the other side? Either way it has to be ran in both. Generator hasnt worked in years, so charging when I am out is not an option. I only boat in a lake, rarely more than .5 mile from the marina. I do have a sound system with a sub installed. Never had any issues with the 6V batteries running out, just not sure if they will have the CCAs i need. Thanks in advance.

DL

[Axios]

6V batteries combined to get 12V banks?
You need 12V batteries, one starting battery bank for the motors and a separate battery bank for onboard use, fridge lights...
Best is one dedicated starting battery bank for each motor, and a separate bank for the rest.

[shrew]

Running 6 volt in Parallel to make 12v using deep cycle golf cart batteries is fairly common for the house bank. It is no common for the starting batteries.

Some folks even run 4 x 6v in Series/Parallel. 2 x 6v wired in Series to double the amperage at 6v. Then the two series banks are wired together in Parallel to make a single large 12v bank.

I would not do this for my starting batteries. I would not run a stereo with a woofer and/or an amp off of my starting batteries if I had no house bank of generator.

If you need all the batteries to start engines, your batteries themselves might be dead.

Do this....

1) Charge the batteries fully

2) Disconnect everything from the batteries and wait 24 hrs.

3) Using a multi-meter, check the voltage on each bank.

The banks should be around 12.8 or 12.9 VDC.

If the banks are reading low, then its' time to change the batteries. I identified a house battery that was reading 11.6 after doing this.

I would install the following:

Starting batteries: 1 x 12VDC (each engine)

House Bank:

a) 2 x 12v Group 31 in Parallel

OR

b) 1 8d

OR

c) 2 x 6v in Series

Look at the total amperage of the house bank and see which best meets you house draw needs. You can add a 3rd battery to the (2x12v) option in parallel. You'd need to add another 2 x 6v (4 x 6v total) if you wanted to increase the 6v Series into a Series/Parallel.

Adding 2 x 4d or 2 x 8D would make a huge house bank if you're not out for long periods of time.