Battery Requirements

[warren.corbin]

Recently purchased 450 Voyager with twin Cummins 450 Diamond Series. Port alternator went out so checked starting batteries and all are shot. The boat currently has the following. All batteries are identical AGM31M, 1150 CCA.

Each engine two 1150 CCA gel batteries in parallel

House has two 1150 CCA batteries in parallel

Genset one 1150 CCA battery

Bow thruster 24 volt so four 1150 CCA batteries in series

So my questions are:

1)Cummins specs call for I think 1100 CCA each engine. For boat operation (local lake) in temps above 60 degrees F, do I need two 1150 CCA batteries in parallel each engine or is one sufficient.

2)For the house batteries, do I need 1150 CCA or can I go lower since I’m interested in lasting time instead of cranking amps.

3) Bow thruster is rarely used on local lake. Can I drop back to two, 12 volt batteries in series instead of the current four batteries?

Any advice is surely appreciated.

[km1125]

Overall, I think it's insane how much capacity that gets put on boats and NEVER used. The engine start batteries need a lot of CCA (or MCA) but very little actual AH capacity. But in the typical install, there's HUNDREDS of amp-hours installed. Same with thruster batteries. House batteries need very little CCA or MCA (unless you have an inverter) but could use a bunch of AH. With not a lot of ingenuity, folks (manufacturers) just keep adding batteries till they get well over the minimum required in either case, and that's how you ended up with your situation.

1)Cummins specs call for I think 1100 CCA each engine. For boat operation (local lake) in temps above 60 degrees F, do I need two 1150 CCA batteries in parallel each engine or is one sufficient.
This is the hardest question to answer, because engines can be "picky" with the voltage drop when starting. The ECU (computer) that controls the engine is what's typically sensitive to the voltage drop. You need to check the actual specs that the engine(s) require and see if it's specifying "cranking amps", "CCA", or "MCA". It's quite likely if they're specifying CCA that's for operation down to 0F, when you could use the MCA rating if you never plan on boating anywhere near 0F.


2)For the house batteries, do I need 1150 CCA or can I go lower since I’m interested in lasting time instead of cranking amps.
If you don't have an inverter, then you don't need anywhere near 1150CCA. The requirement for house batteries is based on how much D.C. power you need, WITHOUT the generator or engines running and not plugged into shore power. How long do you spend "on the hook" where you're only relying on the house batteries?

3) Bow thruster is rarely used on local lake. Can I drop back to two, 12 volt batteries in series instead of the current four batteries?
Again, you'd have to check the specs, but it's very likely you could drop down to two batteries in series to provide plenty of power for the thruster. You might lose a LITTLE bit of thrust but likely not an issue in your described situation. You may not even notice the difference. This is another situation like the engine starters where you never use the A-H capacity that's installed because you only use those thrusters for SECONDS in any situation. If you can get the CCA you need with smaller batteries (group 27 or so) you could likely make that change too.

[bud37]

The thing about your set up is all the batteries are the same, and can be moved around and subbed in for a failure, also no issues with the charging.
Generally engine start and thrusters use the same type of battery and house loads require lots of storage capacity like KM has touched on which is a different battery type.

Is your thruster hydraulic or electric ? The thing about thrusters is you may hardly use them, then comes the time you need them, generally a real problem where you need all the power from your unit to stay safe.

[warren.corbin]

Guys, thanks for your input. The more you suggest, the more I research and work on the learning curve. Following is what I can add:

1) Cummins engine specs call for min CCA 1250 at 0 deg F, MCA 1560 at 32 deg F. So the question still stands, if I'm operating well above these temps am I good with one battery per engine at say 1200 CCA? What I'm thinking is that with two batteries in parallel, you don't know if one is failing so that it ends up dragging the other battery down and killing the alternator. Operating on one battery per engine seems to make it easier to tell if you have a problem with the battery.

2) The bow thruster is electric. I like the idea of having it on the rare occasion when needed, but the need is very seldom. I think I will try it with two batteries in parallel instead of the current four, and see how much use I can get before it runs the batteries low. Any thoughts?

3) For the house batteries, the boat does have an inverter that runs the fridge/freezer and salon entertainment center. I don't know actual cubic feet of fridge, but it is less than half the size of a full size fridge. I plan to spend a night on hook, running the genset part of the time. I know I need the current set-up of two batteries in parallel, just wondering if I need 1150 CCA like the boat currently has.

Bud37 is correct. I think all the current batteries (12) were purchased and installed at same time in 2014. Lot of age on these batteries. If I'm going to replace them all, I just want to size them so that I have the power needed at the most efficient cost. Is there a benefit to matching all the batteries if they are charging off different systems (but some charging together from engine alternators, see below)?

Engine/generator batteries charge from dedicated charger plus engine alternators.

House batteries charge from dedicated inverter/charger plus engine alternators.

Thruster batteries charge from dedicated charger.

Thoughts?

[Midnightsun]

My setup is factory and I do have twin diesels. 2x 1000 cca batteries tied together to form a 2000 cca bank which serves both engine and a thruster. Same setup on other bank which also serves the other engine and another thruster. A dedicated 1000 cca generator battery and finally the house bank which will need to be sized depending on your needs however as mentioned you are looking for AH and not cca when making your choice.

The only battery which is not factory in style is the generator battery because I figured it would be good to have a battery of the same size as the rest in case one failed and I could easily swap it out in a bind.

I guess the idea is you end up with 2000 cca available for starting which is way overkill however as batteries age this number will go down so lots of juice still available after several years. Thusters are only used after engines are running 99.9% of the time so alternators are spinning supplying juice to the banks.

Bottom line is I have 5x 1000cca batteries plus a house bank which has been more than perfect all these years. I happen to have a Cummins centre located on my way to the boat so I tried their batteries 2 years ago when I renewed. Nothing but good to say about them so far. Hmmm, seems like recession/covid and the rest of whatever justifies cost increases has affected these also. They were only $120 cad when I purchased them. https://shop.cummins.com/CSSNAStore/s/p ... ng-battery.

EDIT: Just noticed you are running 24v to the thrusters so the above does not apply. Is it possible to run your thrusters on 12V via a setting or something similar? Would really simplify the battery setup. 4 batteries for a single thruster is absurd unless you want to travel with thruster power once you run out of fuel.