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Old 13-10-2020, 08:31   #1
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Mixing Group 27 and Golf Cart Batteries

Hi all,

I am upgrading a solar and deep cycle house battery system. There is currently a compartment and trays sized to hold two Group 27's. I want to expand this battery bank using this space and some space available in other nearby compartments.

I know the best bang for the buck will be to do all new golf cart batts, but...

What is the downside of having two of these Group 27 Deep Cycles and a bank of 2 golf car batteries in a separate compartment?

The charge controller is a Sun Force 12v 30. The solar array is 425 watts monocrystalline.

I would assume the Group 27's might charge more quickly if the controller sees the bank as one big bank. Will this be the case? Could this result in overcharging of the 27's?

I would rather go all Golf Cart batteries as I'll get more amp hours for the buck, but I'd then have to modify two compartments instead of one, and it seems dumb not to utilize the already-built trays and compartment built for the group 27's.

I could also go all Group 27's, but then I'm sacrificing amp hours/$.

Any help appreciated.
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Old 13-10-2020, 08:55   #2
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Re: Mixing Group 27 and Golf Cart Batteries

The two types.don't have exactly the same charge and discharge properties. If you feel you must get your "use out of them" then the two battery types should be separated by switches into two different house banks. Try to use one bank while you charge the other.

It's a bunch of messing around and extra wire amd switches that cost as much as new batteries anyhow just to get a little use out of old batteries that are already used and will need to be replaced anyhow with all golf car batteries eventually. Might as well bite the bullet now and do it right while you are doing it.

Maybe save one of the group 27s as a starting battery and use a charge control relay to isolate it. Blue Seas Systems has a very nice kit for this with a relay and a dual switch that lets you have separate systems all the time without any extra switches while still allowing emergency combining capabilities.
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Old 13-10-2020, 08:58   #3
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Re: Mixing Group 27 and Golf Cart Batteries

I would probably go with Black Heron's suggestion. Mixing different battery types if necessary won't set your boat on fire but starting batteries work very differently from 6V deep cycle.

You could probably mix them but I would also prefer two banks. If all in one bank I think the 27s would not last all that long being discharged to the level of deep cycles.
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Old 13-10-2020, 09:02   #4
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Re: Mixing Group 27 and Golf Cart Batteries

Don't mix different battery types or even different battery ages.

If you can't find space for 4x golf cart batts, then you will need to stay with all Group 27's.


You could have two smaller banks as others suggested, but that brings its own problems, not to mention complexity. This will NOT work better than 4x Group 27's.


I used 8x Group 27's (Trojans) for years. They don't last very long, but they get the job done. This year I went to a lot of expense and trouble to recut my battery boxes so I can use 8x Trojan golf cart batts.
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Old 13-10-2020, 09:06   #5
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Re: Mixing Group 27 and Golf Cart Batteries

Thanks all. I appreciate it. To clarify, I'm buying all these batteries new. Not using any old batts. And these Group 27's are supposedly real "deep cycle" and not hybrids or starting batts. They are rated in amp hours and not CCA. They're not as deep cycle as the golf car batts I guess though.

I'm wondering if I should just do this whole system with deep cycle Group 27's.
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Old 13-10-2020, 09:19   #6
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Re: Mixing Group 27 and Golf Cart Batteries

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Originally Posted by Peregrine1983 View Post
Thanks all. I appreciate it. To clarify, I'm buying all these batteries new. Not using any old batts. And these Group 27's are supposedly real "deep cycle" and not hybrids or starting batts. They are rated in amp hours and not CCA. They're not as deep cycle as the golf car batts I guess though.

I'm wondering if I should just do this whole system with deep cycle Group 27's.
There's no such thing as real "deep cycle" Group 27's. They are basically "leisure batteries", something half way between deep cycle and start batts. The best ones I know are the Trojans I used to use -- 27TMX. But they more or less do the job. If there is really no way to use 4x golf cart batts, I would just go that way.

You can extend their lives by being very careful not to discharge below 50% or better 60%. They are much less tolerant of that than gold cart batts. I used to get about 2 years out of a set, sometimes a third year but with reduced capacity.
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Old 13-10-2020, 09:25   #7
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Re: Mixing Group 27 and Golf Cart Batteries

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There's no such thing as real "deep cycle" Group 27's. They are basically "leisure batteries", something half way between deep cycle and start batts. The best ones I know are the Trojans I used to use -- 27TMX. But they more or less do the job. If there is really no way to use 4x golf cart batts, I would just go that way.

You can extend their lives by being very careful not to discharge below 50% or better 60%. They are much less tolerant of that than gold cart batts. I used to get about 2 years out of a set, sometimes a third year but with reduced capacity.

Thanks Dockhead. That's kind of what I suspected about them not being real deep cycle. I want something I can beat up and really discharge if I have to. I think I'm going to have a hard time getting my hands on those 27TMX's around here before I need them.



It's too bad the true deep cycle batts don't come in the Group 27 form factor. Must be the dimensions of the plates or something?
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Old 13-10-2020, 09:29   #8
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Re: Mixing Group 27 and Golf Cart Batteries

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. . . It's too bad the true deep cycle batts don't come in the Group 27 form factor. Must be the dimensions of the plates or something?
Exactly. If you look at a golf car batt and look at a Group 27, you see the plates are more than double the thickness, and they are taller. Remember that golf cart batts are 6v.
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Old 13-10-2020, 09:49   #9
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Re: Mixing Group 27 and Golf Cart Batteries

Thanks everyone. Looks like I'm going to go with the original plan for all golf cart batts. Just going to have to do some modifications to fit them in the Group 27 compartment.
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Old 13-10-2020, 10:06   #10
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Re: Mixing Group 27 and Golf Cart Batteries

Quote:
Originally Posted by Peregrine1983 View Post
Thanks all. I appreciate it. To clarify, I'm buying all these batteries new. Not using any old batts. And these Group 27's are supposedly real "deep cycle" and not hybrids or starting batts. They are rated in amp hours and not CCA. They're not as deep cycle as the golf car batts I guess though.

I'm wondering if I should just do this whole system with deep cycle Group 27's.
If you're going all new I would if at all possible, go with the GC2 size 6V golf cart batteries. As Dockhead points out, there are no true deep cycle group 27 batteries, or none that I've ever encountered.

It wouldn't be that difficult to fabricate a new battery box for the GC2 size if it will fit in the space you have. I was able to fit a larger battery box by replacing a thick plywood box with a stronger, stainless steel box. I lined the box with acid neutralizing pads to deal with any possible spills and corrosion. With very minor additional mods was able to fit 6 x GC2s in the space that originally held only 4.
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Old 13-10-2020, 22:42   #11
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Re: Mixing Group 27 and Golf Cart Batteries

Well there are no real 'true deep cycle' flooded group 27 batteries. With Rolls-surrete being a possible exception

https://www.dcbattery.com/rollssurrette_27m105.pdf

AGM's Like Lifeline, perhaps some others, do qualify.

If one wants to make use of older flooded 'deep cycle' with new series GC-2's in parallel, it is likely the 27's, if still healthy, will have lesser resistance and higher resting voltage, and will essentially support more of the load and take more of the charging amperage, and be used up faster.

But the GC-2s in such a situation might never get fully charged, or be consistently overcharged, and when the 27's die and you want to replace them with new GC-2s.... New and old GC-2s will be somewhat similarly mismatched, but a bit less so, and Unideal will continue, perhaps with little consequence, or perhaps not.

Also in my experience, marine flooded 27's, take forever at absorption voltage for specific gravity to max out, in deep cycle duty.....Likely far more time than healthy New flooded GC-2's when held at the same voltage. All the flooded 27's and 31s I've treated like true deep cycle batteries, when I checked specific gravity, proved they were unhappy in such duty, and even if the solar got them to 14.7 by 10Am and held it until late afternoon, the specific gravity never maxed out at predetermined maximums. Even when I set float to 15.3v, after 4 hours at 14.7v, they remained below prerecorded maximums.

The flooded 31 I treatred best achieved only 550 deep cycles before it was just not worth the efort to keep cycling it deeply, but in shallow cycle duty it lasted another ~300 cycles with minimal care regarding charging properly. Used a LOT of water, chewed up the concrete under it. Stunk like a fried rotten egg for hours each day.

Exactly how new and old and different type interact in use has many variables, variables best eliminated buy not mixing and matching in the first place.

But its hard to dismiss batteries with life left in them just because they do not match with what would be ideal. I've got 4 such batteries on workshop floor, feeding on solar, taking some load off the grid, and the 15 amp 120vAC breaker.

Mainesail's 'what is a deep cycle battery' is good reading, when someone believes their flooded 27, which says deep cycle on it, is an actual deep cycle battery.

One can deep cycle a stating battery, it does not make it a deep cycle battery, only a battery being deeply cycled.

https://marinehowto.com/what-is-a-deep-cycle-battery/

When I had one flooded bank and one AGm bank, I had two 1/2/both off switches, one for loads and one for charging sources, and could cycle one and charge the other, easily enough, then swap them the next day. Lots of room for human error though.
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Old 14-10-2020, 16:32   #12
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Re: Mixing Group 27 and Golf Cart Batteries

Hi, jack: My new-to-me Carver 28 has 2 group 31s which serve as start/house batts. Dock Queen style. My idea is to revamp the box for 4 GC batteries to serve as both start/house. The boat has 2 220hp engines.
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Old 14-10-2020, 17:03   #13
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Re: Mixing Group 27 and Golf Cart Batteries

Another possibility if you have the height in the compartment is to get a pair of L16s, J305s or similar as opposed to 4 golf cart batts.
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Old 14-10-2020, 21:42   #14
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Re: Mixing Group 27 and Golf Cart Batteries

Quote:
Originally Posted by Peregrine1983 View Post
Hi all,

I am upgrading a solar and deep cycle house battery system. There is currently a compartment and trays sized to hold two Group 27's. I want to expand this battery bank using this space and some space available in other nearby compartments.

I know the best bang for the buck will be to do all new golf cart batts, but...

What is the downside of having two of these Group 27 Deep Cycles and a bank of 2 golf car batteries in a separate compartment?

The charge controller is a Sun Force 12v 30. The solar array is 425 watts monocrystalline.

I would assume the Group 27's might charge more quickly if the controller sees the bank as one big bank. Will this be the case? Could this result in overcharging of the 27's?

I would rather go all Golf Cart batteries as I'll get more amp hours for the buck, but I'd then have to modify two compartments instead of one, and it seems dumb not to utilize the already-built trays and compartment built for the group 27's.

I could also go all Group 27's, but then I'm sacrificing amp hours/$.

Any help appreciated.
Basic principle - never mix battery types - and that includes the same model new with old. If you want to mix, then separate with a splitter, or relay or switch etc.
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Old 15-10-2020, 15:39   #15
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Re: Mixing Group 27 and Golf Cart Batteries

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Originally Posted by laika View Post
Another possibility if you have the height in the compartment is to get a pair of L16s, J305s or similar as opposed to 4 golf cart batts.
Intriguing. Don't know about the J305s so will research. I wonder what will fit easier?
My other issue is whether a large suite of house batts will do double duty as starters. I don't see why not - it would simplify life considerably.
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