Group 24 installed with group 27 batteries

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Mooney 78865

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I have a Georgetown class A that has a 4 battery capacity.  When we picked up the coach the dealer had a pair of group 24 batteries installed. We subsequently replaced them with a pair of group 27.  I still have the two new group 24 batteries and am wondering if it would be ok to use them for additional capacity wired in parallel. Or would it cause an issue with the charging system(s)
 

Isaac-1

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Batteries should always be installed in matched sets, same size, brand, and age, preferably same lot number.  Battery electrolyte chemistry changes with battery age, as well as exact battery design.      Mixing batteries will likely result in some being under charged and other over charged, which is bad in the long run.
 

Gizmo100

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It's my understanding that while it would work you would be less than happy with the results....

You could hook them up as a 2nd set of batteries and use a switch to go back and forth as needed. Of course you would have to add extra cables and a switch. But is it worth all that trouble?
 

Henry J Fate

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There is tons of info online about this subject. I personally tend to disagree with some of it but there are things to be aware of when charging a bank of batteries that are either a different age, different type or different size. The battery life expectancy and the quality of the battery can be compromised if they are in a circuit with different batteries. Generally it is best to put 4 batteries in of the same age, size and type. If you do choose to mix batteries, keeping alike batteries together is important. If for example you had four 6 volt batteries for a 12 volt circuit and two were new and two were used with the same usage, it would be best to place the two new ones in series and the two old ones in series then place the old and new in a parallel 12 volt circuit. The problem is that the charging and discharging won't be in sync between all of the batteries which creates different charge cycles and profiles. The inverter charger won't know what state each battery is and nor does it care. It assumes that the voltage it reads is the voltage of all the batteries which is a good guess if all the batteries are the same age, type and size. It gets a little tricky especially if there are large differences in battery conditions. I will admit that I have mixed batteries but I also have carefully watched them. I did find a battery overcharged slightly at one point but it wasn't of great concern.

I currently have two house batteries alike and a older deep cycle battery I use for starting. All three batteries are charged off the engine alternator and I have not noticed any issue with that. I also combine the starter battery with the house batteries when idle for extended periods and plugged in to charge the starting battery. I have not had any issues at all. All three batteries are doing well and have good capacity.

My suggestion is too keep the batteries alike but on the other hand, if you have good batteries sitting around and the room to install them, use them but be aware of possible complications.
 

Mooney 78865

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I was thinking that the different capacity could be an issue when charging. I guess I can use the two group 24 batteries as cores, but it seems such a waste...
 

Gizmo100

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Mooney 78865 said:
I was thinking that the different capacity could be an issue when charging. I guess I can use the two group 24 batteries as cores, but it seems such a waste...

I feel your pain..When we upgraded the battery on our TT I was in the same position. I decided to hang on to the battery for use either with my cargo trailer or hopefully as a battery for a boat once we get moved.
 

ChasA

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I like Gizmo 100's idea of a switch. Many boats have 2 banks and switches to control the banks are readily available in marine stores.
 

John From Detroit

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Batteries are kind of confusing for most
Paralling a group 24 or two with a group 27 or 31 or two is just fine. the batteries will share both load and charging current ACCORDING TO THEIR ABILITY or NEED. I've seen all sorts of "Don't do it because of This or That and the fact is the things they warn about are basically IMPOSSIBLE.

Now when you put batteries in SERIES (IE GC-2's takes two in series to make 12 volts  THEN Each battery in the pair needs to match it's mate. But Pairs A need not match Pair B need not match the Group 27 off to the side of it.  THe reason for this is easily explained because each of the GC-2's in the pair are one half of a 12 volt battery. and clearly both halves have to match.

But when you are talking parallel. Do whatever you want. they batteries will work it out so long as the jumpers are big enough.
 

Mooney 78865

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But when you are talking parallel. Do whatever you want. they batteries will work it out so long as the jumpers are big enough.
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John From Detroit, your response is pretty much what I am getting elsewhere as well.  The way it was explained to me was if they are like batteries, (they are) and run in parallel, you are only increasing capacity. A larger fuel tank if you will.  The charger only sees voltage. So while charging it doesn't care about the number of cells, or the size of the cells, it charges at what ever amp hour to return the entire battery bank to 12 volts. Do I understand it correctly?
 

John From Detroit

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You are basically correct.  One thing is of course the more battery capacity (Technically it's all one battery when hooked up) the longer it can go between recharges and the longer it will take to charge.. Though odds are you won't really notice that last.
 

Henry J Fate

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That is a fair interpretation. Any series connection between batteries should be batteries of the same type, capacity, age, etc. Placing that battery series into a circuit parallel to another set of series batteries should be fine. Always keep an eye on things after the install and be sure the additional batteries are in fact good.

What would not be good would be to take a new battery and place it in series with an old battery.
 

solarman

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Isaac-1 said:
Batteries should always be installed in matched sets, same size, brand, and age, preferably same lot number.  Battery electrolyte chemistry changes with battery age, as well as exact battery design.      Mixing batteries will likely result in some being under charged and other over charged, which is bad in the long run.

correct..

you can mix and match if you want to of course, just don't expect much life or performance from the set..

 

Gary RV_Wizard

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Agree with John 100%. While the ideal is that all batteries are identical in capacity and condition, the reality is that small differences are insignificant except in huge battery banks (dozens or hundreds of batteries).  Group 24 and Group 27 are only modestly different in capacity and in this case the condition appears to be similar, so in this case there is no reason not to add the two extra batteries.

"Don't mix batteries" is a rule of thumb to prevent the unknowledgeable from inadvertently making a mistake. It's not a religious admonition.
 

Mooney 78865

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Thanks folks!  I was not thrilled on having to use them as "cores".  I have no need for them for any other application.
 

John From Detroit

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solarman said:
correct..

you can mix and match if you want to of course, just don't expect much life or performance from the set..

With batteries mixed in parallel. I'd expect the same life as if they were all matched.
NO Difference.  The only "Danger" and in this it does not matter if they are mixed or matched is if one battery has a shorted cell.  and again even in this mixed or matched it makes NO DIFFERENCE.. all the "OH {bad thing} will happen. are MYTHS. they do not happen. can in fact not happen. It's that simple.  IF you think about it you will realize it  But I do not wish to type the myths out because they CAN NOT happen.
 

Isaac-1

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John, I don't dispute that mixing in series is far worse than mixing in parallel, but I do disagree that mixing in parallel makes no difference.    The thing to remember about batteries is that they act as resistors, more importantly they act as variable resistors where the resistance changes with age, chemistry and state of charge.    If you mix batteries of differing types the flow of electricity will not be evening distributed, which may be self correcting to a degree depending on where the mismatch is in the variability of the charge, or it may lead to some cells being persistently over charged and others persistently under charged, which is where the whole bad thing comes into play.   
 

Gary RV_Wizard

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Some batteries may take more amps and other less, but it doesn't really matter in a parallel battery bank. They bulk current flows down the cables from post to post and each battery accepts what it can.  It's current path is completed across the battery to its negative ost and on through the negative cables (also post-to-post).  It would take a major difference  in battery resistance to have a material effect. The charger sees the average voltage and total amp draw of the entire bank.

The only risk in combining batteries like this is if one is substantially different in condition than the others, either shorted or a high resistance cell. That battery may overheat and boil dry.
 

John From Detroit

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Isaac-1 said:
John, I don't dispute that mixing in series is far worse than mixing in parallel, but I do disagree that mixing in parallel makes no difference.    The thing to remember about batteries is that they act as resistors, more importantly they act as variable resistors where the resistance changes with age, chemistry and state of charge.    If you mix batteries of differing types the flow of electricity will not be evening distributed, which may be self correcting to a degree depending on where the mismatch is in the variability of the charge, or it may lead to some cells being persistently over charged and others persistently under charged, which is where the whole bad thing comes into play. 

If you mix different TYPES. then yes. there is risk but a group 24 and a group 27, 29 and 31 of the same type .. Well they will work it out.

WHY (Ok I hoped I would not have to do this) State of charge determines VOLTAGE on lead acid batteries so if one is at a higher state of charge it will not accept current (When charging) till the others catch up an if providing power it will provide all of it till it catches up with the others going down. Once that happens they will always remain in perfect LOCK STEP providing according to their ability and accepting according to their need.

IE if providing 200 amps from a Group 24 and a group 31 you wlll see aboutg 70-75 amps from teh 24 and the rest from the 31  Cause if you look at the amp hours.. Well that's also the amp hour ratings of those batteries.
 

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