Mixing Amps on a House Bank?

[Roniszoro]

Hi All:


I have always had a house bank with batteries with the same amps e.g. 4 Group 31s. But now I'm looking at purchasing a boat and most that I'm considering have smaller banks than I would like. So I would be adding batteries. Do all the batteries have to have the same amps in a house bank? Can I have, for example, two Group 27s and two Group 31s all wired together in a house bank?


Thank you in advance for your input.

[SV_Harbinger]

My first thought would be 12vdc is 12vdc, but then I thought that the larger batteries may beat up the smaller ones, especially while charging. Not sure though I'm absolutely not an electrician (actually if you see me carrying a wire and tools, you should probably take them from me before I hurt something/someone/myself)
Someone here however should be able to get an answer for you, that you can trust but for what it's worth I would say no, mixing ah in the same bank is a probably not so good idea...

[Cheechako]

I ran a mix of Gel and Wet batteries, and they were not the same size either in the Caribe for 3 years without issues. Is it the best scenario? Probably not, but the boat was sold with the batteries still intact. I think the biggest possible issue is the smaller batteries may overcharge while you are trying to fill the bigger batteries if they are a lot different in capacity,,,?

[kenbo]

It's not the ideal set up but it will work. But make sure that all the batteries are from the same manufacturer, the identical chemistry and the same age. Even when the batteries are "identical" the cables and connections create significant resistance differences within a bank. So give thought to the cables as well.

[SV_Harbinger]

That's what I was thinking too but I've always just had all banks of the same size and replace all at once if/when the good bad..

[Roniszoro]

I would not combine battery types. All would be gel. What I'm wondering is can I have 27s and 31s together in a house bank?

[kenbo]

Originally Posted by Cheechako

I ran a mix of Gel and Wet batteries, and they were not the same size either in the Caribe for 3 years without issues. Is it the best scenario? Probably not, but the boat was sold with the batteries still intact. I think the biggest possible issue is the smaller batteries may overcharge while you are trying to fill the bigger batteries if they are a lot different in capacity,,,?

Me thinks you were very lucky especially mixing gel and wet with their very different charging profiles. I have wet in the house bank and AGM (Optima) for start and they're combined during charging. So far so good.

[kenbo]

Originally Posted by Roniszoro

I would not combine battery types. All would be gel. What I'm wondering is can I have 27s and 31s together in a house bank?

Yes, if the same age and manufacturer. The internal resistance will be similar enough to work.

[Cheechako]

Originally Posted by kenbo

Me thinks you were very lucky especially mixing gel and wet with their very different charging profiles. I have wet in the house bank and AGM (Optima) for start and they're combined during charging. So far so good.

Maybe, but you have to realize that 95% of the time cruising (without solar) your batteries are living in some state of discharge. Often running a very deep cycle every day. Then you attempt to charge with wind, gen or alternator for an hour or so, but often never really get full charged... as everyone is waiting in the dingy to go explore town! So the biggest problem is just getting a charge in them, rather than a specific profile.
Combined, I guess the batteries are floating to an equilibrium amongst themselves...

[GrowleyMonster]

NOT a good idea, no. But it has been done and is being done and will be done, and knock on wood, usually works okay. Scenario. You have a bunch of old batteries of same type, similar ratings and age, but you want new batteries. You install new ones but before taking the old ones in for the core refund, you think, Hmmmm.... what do I got to lose, by taking these old ones and hooking them up into a separate bank? Just use them until they are toast, and I still got the new ones, with only light use on them. Okay, sure, do that. Let's say you have a bank of four old batteries and two are toast, and you want to just add two more for four in parallel. Unwise. Better to split them into two banks and use a A/B switch.



Bottom line is you can generally work something up that does not put different batts together. Sure, a big bank is somewhat more efficient than two smaller ones, but it isn't a dealbreaker. I would not mix them together in one bank, me.

[Roniszoro]

[QUOTE=GrowleyMonster;2673505]NOT a good idea, no. But it has been done and is being done and will be done, and knock on wood, usually works okay. Scenario. You have a bunch of old batteries of same type, similar ratings and age, but you want new batteries. You install new ones but before taking the old ones in for the core refund, you think, Hmmmm.... what do I got to lose, by taking these old ones and hooking them up into a separate bank? Just use them until they are toast, and I still got the new ones, with only light use on them. Okay, sure, do that. Let's say you have a bank of four old batteries and two are toast, and you want to just add two more for four in parallel. Unwise. Better to split them into two banks and use a A/B switch. QUOTE


Not what I am trying to do.

I'm looking at boats with house banks of 2 batteries. I want a 4 battery house bank. Let's say, for this discussion, that the two current batteries are newish Lifeline Group 27s. Can I add two Lifeline Group 31s or do I need to stay with adding two Lifeline 27s? That is the question.

[kenbo]

[QUOTE=Roniszoro;2673529]

Originally Posted by GrowleyMonster

NOT a good idea, no. But it has been done and is being done and will be done, and knock on wood, usually works okay. Scenario. You have a bunch of old batteries of same type, similar ratings and age, but you want new batteries. You install new ones but before taking the old ones in for the core refund, you think, Hmmmm.... what do I got to lose, by taking these old ones and hooking them up into a separate bank? Just use them until they are toast, and I still got the new ones, with only light use on them. Okay, sure, do that. Let's say you have a bank of four old batteries and two are toast, and you want to just add two more for four in parallel. Unwise. Better to split them into two banks and use a A/B switch. QUOTE


Not what I am trying to do.

I'm looking at boats with house banks of 2 batteries. I want a 4 battery house bank. Let's say, for this discussion, that the two current batteries are newish Lifeline Group 27s. Can I add two Lifeline Group 31s or do I need to stay with adding two Lifeline 27s? That is the question.

Depends on what you mean by "newish", I've seen 6 month old AGM's with really reduced capacity because they sat partially discharged.

[billknny]

So now you have your answer...

Some people say, "Sure, go ahead." Others say, "It's a bad idea."

From an outsider's perspective you are back to square one and get to pick the answer YOU like best, just as if you had never posted! But do notice that many people have jumped in with an answer, and none of them have bothered to ask how you are going to use your boat. Or what your electrical system looks like. All that actually matters to getting a good recommendation that will work for you.

Of course if you did any research, you have already found every recommendation from every expert is the same: For optimum performance and longevity every battery in a bank should be identical in size, type, manufacturer and age.

Of course, experts have been know to be wrong. And you might not care about optimum performance, anyway.

Are you feeling lucky?

[skipmac]

Originally Posted by Roniszoro

I would not combine battery types. All would be gel. What I'm wondering is can I have 27s and 31s together in a house bank?

Yes, you can and the batteries won't die immediately or catch on fire.

[skipmac]

Originally Posted by billknny

So now you have your answer...

Some people say, "Sure, go ahead." Others say, "It's a bad idea."

From an outsider's perspective you are back to square one and get to pick the answer YOU like best, just as if you had never posted! But do notice that many people have jumped in with an answer, and none of them have bothered to ask how you are going to use your boat. Or what your electrical system looks like. All that actually matters to getting a good recommendation that will work for you.

Of course if you did any research, you have already found every recommendation from every expert is the same: For optimum performance and longevity every battery in a bank should be identical in size, type, manufacturer and age.

Of course, experts have been know to be wrong. And you might not care about optimum performance, anyway.

Are you feeling lucky?

Certainly the ideal would be all the same chemistry, size, brand and age. However from a real world, practical perspective:

- The least desirable is to mix different battery chemistries IE AGM, gel, FLA. Doing so would likely result in early death for the battery receiving the least ideal charge profile. The boat still won't explode and the batteries won't die immediately, just soon or much sooner than they might have in a better situation.

- Size. Not nearly as critical as chemistry unless you're mixing really different batteries like a deep cycle 4D with a motorcycle starting battery. Batteries are charged based on the voltage difference and available amps. Assuming all the same size batteries in any series connection then they will charge based on state of discharge. A fully charged small battery will not overcharge in parallel with a discharged large battery of the same chemistry. Again, not ideal but mixed sizes will live together quite well.

- Age. If you have some that are very old and almost dead I would not mix them with nice new batteries. There is definitely potential for problems here. However if I had a couple of two year old batteries that tested well, held charge, etc I would not toss them out if I wanted to add a couple of brand new batteries to expand capacity.