Another Battery Question

I posted a battery question on an early thread but didn’t explain it right. I have a 2004 280 Sundancer. My port battery went bad. I replaced it with the same type, a flooded lead acid 1050 CCA from West Marine. There are three batteries total. Two 1050 CCA, one on the starboard side and one on the port side, which is the one I replaced. The house battery is a 840. There’s a dual battery switch and a separate house battery switch. Mostly everything I have read says to replace all the batteries at the same time. Is it ok to have a different size battery for the house battery? And what size battery should I use for the house battery?

Well, having a different capacity battery in there is ok. However, it sounds like you have a starting battery as the house battery based on the high amp rating. That is less than ideal. If it is a starting battery, it it made for quick high amp discharges, not long slow deep discharges. If you continuously draw it down low, it is also going to only live a short life.

1132MM said:

I posted a battery question on an early thread but didn’t explain it right. I have a 2004 280 Sundancer. My port battery went bad. I replaced it with the same type, a flooded lead acid 1050 CCA from West Marine. There are three batteries total. Two 1050 CCA, one on the starboard side and one on the port side, which is the one I replaced. The house battery is a 840. There’s a dual battery switch and a separate house battery switch. Mostly everything I have read says to replace all the batteries at the same time. Is it ok to have a different size battery for the house battery? And what size battery should I use for the house battery?

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The advice about replacing them at the same time is when they are part of the same battery bank. It sounds like you have 3 separate banks, which means they can be replaced separately when needed. However, it seems unusual for a Sea Ray to have separate banks. Normally the house and one of the engines are on one bank together. But not sure about your boat.

1132MM said:

I posted a battery question on an early thread but didn’t explain it right. I have a 2004 280 Sundancer. My port battery went bad. I replaced it with the same type, a flooded lead acid 1050 CCA from West Marine. There are three batteries total. Two 1050 CCA, one on the starboard side and one on the port side, which is the one I replaced. The house battery is a 840. There’s a dual battery switch and a separate house battery switch. Mostly everything I have read says to replace all the batteries at the same time. Is it ok to have a different size battery for the house battery? And what size battery should I use for the house battery?

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As mentioned when in separate banks, replacement can be done as needed. As for the house battery, I had a 340 that I put an 8D in for the house battery. It was the best thing I ever did for that boat. I had a generator which required a battery and instead of sharing it with the port engine I shared it with the house battery. So I only needed to run the generator in the heat of the day while on the mooring.

Thanks for the responses. It does seem like the house battery and the port are on the same bank. They’re grounded together. However I can’t find a 1050 CCA dual purpose to keep the amperage the same on that bank. It’s very confusing.

That boat doesn't have a house battery. Make sure the bank with the 2 batteries have the same battery of the same age.

1132MM said:

Thanks for the responses. It does seem like the house battery and the port are on the same bank. They’re grounded together. However I can’t find a 1050 CCA dual purpose to keep the amperage the same on that bank. It’s very confusing.

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That makes sense and is how Sea Ray normally sets up the batteries. Shop around and by the largest pair of Dual purpose you can find. To be honest, if you have a pair of them, the CCA is not an issue for a 4.3l v6 engine. You will have plenty of CCA for starting. Look for the highest amp hour ratings you can find and it will maximize your house battery capacity, if that is what you are trying to achieve.

Ok thanks! Do you think it’s fine to have two 1050 Starting on the same bank?

Typically it's best not to have batteries in parallel because one inherently will always charge the other and is best to have a larger battery instead. That said boats have bat's in parallel all of the time. The down side is you have to replace them more often because one is always charging the other.

Thanks guys I appreciate the responses!

1132MM said:

Ok thanks! Do you think it’s fine to have two 1050 Starting on the same bank?

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Yeah, but way overkill for a single 4.3L six. If its battery life while engines/generators off, then its not starting batteries you want. They trade off high cranking capacity (which you don't need) for lower ability to discharge deeply (they will not last long at all if they are deeply discharged on a regular basis).

I happened to run in to marine mechanic at the marine supply store today. He said the 1050 starting is ok to be on the same bank as a dual purpose. He said it comes down to reserve minutes for the house battery. He said the 2004 280 dancers do have a house battery usually on the same bank as the port starting battery. He recommended a dual purpose for the house battery that has at least 160 reserve minutes.

1132MM said:

I happened to run in to marine mechanic at the marine supply store today. He said the 1050 starting is ok to be on the same bank as a dual purpose. He said it comes down to reserve minutes for the house battery. He said the 2004 280 dancers do have a house battery usually on the same bank as the port starting battery. He recommended a dual purpose for the house battery that has at least 160 reserve minutes.

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That is bad advice, sorry. If two batteries are connected to the same charger, and one has lower capacity, they will charge at different rates. Both batteries on the same bank should be as identical as they can be. Ideally same exact battery bought at the same time.

The smaller battery will be charged "full" faster than the larger one, resulting in the smaller one continuing to be overcharged until the large one is done and they both come up to full voltage. That will kill the smaller one much faster.

The same issue happens if you have an old battery that is not getting to full charge, and you pair it up with a brand new battery. The charger will keep charging until the old battery is up to charge, meanwhile the brand new one will be overcharging all that time.

Maybe an extreme example.

Lets say you have two bad batteries on a bank. They won't go over 11 volts no matter how long you charge them. They are dead. So you decide to replace just one for now and buy a brand new battery and swap one out.

First thing that will happen is the new battery will start to "charge" the dead one because its 12.6v will discharged into the 11 volt battery until the two are equal. Meaning your brand new battery will discharge itself to "dead" state.

But you probably will connect your charger when you put the new one it. So then what happens is your charger will see a bank that has maybe 11.8v, so it will pump up the amps and volts and try to bulk-charge the bank -- maybe 15v at 20amps being fed to both batteries. Your brand new battery will boil away at 15v and the dead battery won't come up much above the 11v. So meanwhile your brand new one is getting cooked.

1132MM said:

I happened to run in to marine mechanic at the marine supply store today. He said the 1050 starting is ok to be on the same bank as a dual purpose. He said it comes down to reserve minutes for the house battery. He said the 2004 280 dancers do have a house battery usually on the same bank as the port starting battery. He recommended a dual purpose for the house battery that has at least 160 reserve minutes.

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In short any two batteries that are being tied together, in parallel, must be the same exact type Ah, CCA, MCA, RC (reserve capacity) rating and Group size. Like I said above, it's easier to just get a larger battery then deal with this. A group 31 deep cycle will last you a very long time if charged with a modern charger.

The reason that they need to be the same is simple, the charger isn't going to know the difference between the lighter battery and the heavier one. So the lighter one will charge quickly and the charger will go to float and then the light battery will be charging the heavier one and it becomes a viscous cycle then one day your batteries are completely dead (2nd or 3rd year) and need to be replaced and you don't know why. That is why they need to be the same.

I run a pair of deep cycles on my single engine 502 because I run a large amp for the stereo. Never a problem with starting the engine.

1132MM said:

I happened to run in to marine mechanic at the marine supply store today. He said the 1050 starting is ok to be on the same bank as a dual purpose. He said it comes down to reserve minutes for the house battery. He said the 2004 280 dancers do have a house battery usually on the same bank as the port starting battery. He recommended a dual purpose for the house battery that has at least 160 reserve minutes.

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I agree also that mechanic is wrong in his advise.
First in your boat you should have two banks of batteries and a dual bank battery charger that will charge each bank independently.
For your boat obtaining batteries based upon CCA and worrying about CCA is not relevant to your needs. You should be considering batteries based upon "dual purpose" and "Amp Hour" ratings. Your batteries should be either Group 27 dual purpose or Group 31 dual purpose.
Sea Ray boats really don't have traditional "house bank" battery configurations. The duties of the batteries in the case of a dual engine dual bank battery boat are shared across all of the loads. Sea Ray tries to dedicate the cabin loads on one bank and boat operations loads on the other bank but critical loads like bilge pumps are split between the two banks. I would say that I'd be more concerned that the daily use loads be split equally across all battery banks. You should know your demands on the battery banks before setting the selector switch on "both". "Both" by the way ties both battery banks together in parallel consequently all of the charging sources (battery charger, alternators) are now feeding the same circuit which may not be optimal for efficient charging. I would reserve the "both" setting for when the system isn't performing correctly.
OK, so regarding mixing battery sizes, ratings, and age across your battery system. You will have poor results in battery performance, maintenance, and life if you should either mix battery sizes or differing ages in a single battery bank connected in parallel. The charging system will prioritize the demand of the battery that fits the charging profile and ignore the battery that is below the profile. In such a mixed system demanding service from the bank will depress the smaller/weaker battery and cascade early failure then you add another new battery with the old new battery and start that failure mode again.
So, first you really need to ensure the charging systems are healthy and perform to specifications; without this throwing money at batteries is simply throwing money away; those batteries will fail prematurely. Secondly, I would recommend replacing all of the batteries with new Group 27 Dual Purpose batteries and be done with the issue.

Thanks I think I’ll go with Creekwood, SKybolt, and ttmott’s advice and do all dual purpose batteries.

1132MM said:

Thanks I think I’ll go with Creekwood, SKybolt, and ttmott’s advice and do all dual purpose batteries.

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that is solid advice