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Old 09-26-2019, 10:31 AM   #1
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Battery question

When we purchased our boat it had as a house bank - 2 group 24s and 2 group 27s. Now it's time for new batteries and was wondering if they all should be the same group. Is there any problems with different groups together?
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Old 09-26-2019, 10:43 AM   #2
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I would have all the batteries in one bank the same type, same size and same age.
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Old 09-26-2019, 10:49 AM   #3
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As Dave said, the same batteries the same age is best. Since you're changing them, you might investigate golf cart batteries which are frequently used in a house bank.
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Old 09-26-2019, 11:32 AM   #4
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Originally Posted by Ken E. View Post
you might investigate golf cart batteries which are frequently used in a house bank.

This.....4 will give you a substantial 440amp hour house capacity in about the same footprint. Your 24's and 27's were likely automotive batteries and poorly suited for a house bank..
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Old 09-26-2019, 12:17 PM   #5
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Yes do look at GCs
https://marinehowto.com/wp-content/u...le-Battery.jpg
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Old 09-26-2019, 12:18 PM   #6
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Depending on available footprint vs height, L16 6 volts can also be used instead of the golf cart sized ones. They're taller, but if the height is available, they can let you fit more battery in the same footprint (or the same in less footprint). Golf cart AGMs are typically around 220 - 260ah / 6v, L16s are usually in the 370 - 420ah ballpark.
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Old 09-26-2019, 12:26 PM   #7
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I agree that same type, same age, same size is the best. If for some reason you can't fit the same size, that I think is less of an issue than same type and same age.


FWIW, GRP 24 and GRP 27 are really not deep cycle batteries. For a house bank, I think you may be better served with deep cycle batteries. So as Ken mentioned, consider changing over to golf cart batteries. My guess is that when new, that battery combination you have would have given you around 340Ah. 4 GC batteries should give you around 400+ Ah of capacity.
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Old 09-26-2019, 12:28 PM   #8
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Depending on available footprint vs height, L16 6 volts can also be used instead of the golf cart sized ones. They're taller, but if the height is available, they can let you fit more battery in the same footprint (or the same in less footprint). Golf cart AGMs are typically around 220 - 260ah / 6v, L16s are usually in the 370 - 420ah ballpark.

That is what I did. But as was discussed in another thread, those L16s are pretty heavy. GC2 batteries are a lot easier to move around.
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Old 09-26-2019, 12:30 PM   #9
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Originally Posted by gonesailing13 View Post
When we purchased our boat it had as a house bank - 2 group 24s and 2 group 27s. Now it's time for new batteries and was wondering if they all should be the same group. Is there any problems with different groups together?

Do you have one or 2 engines?
What is your access like for battery maintenance?
Do you have an inverter/charger?
What about a separate diesel generator?

Is your alternator high output or just stock OEM?


If you go with a bigger bank, you also need to be able to charge them.
Four standard golf cart batteries is about bare minimum for overnights with refrigeration and hoping to start the main engine the next morning.
Now if you just marina hop, replacing what you have with new would be ok.
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Old 09-26-2019, 12:32 PM   #10
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Purists will disagree, but I suspect that mixing battery sizes is no problem. But a more significant consideration is having true deep cycle batteries for house use.

True deep cycle batteries have thicker plates, more room for electrolyte above and below the plates and fill caps. Most so called deep cycle or dual purpose 12V batteries do not meet all of these requirements.

The only type of battery that is true deep cycle (except for a few very expensive brands) is golf cart batteries and some sister batteries such are used for floor polishers- L16s. The golf cart battery is ubiquitous, millions are sold each year and are available at Costco, Batteries Plus, golf cart shops and others for about $100 each. They are 6 volts which means you use them in pairs, wired in series which provides about 220 amp hours at 12 volts.

All of the above applies to FLA- flooded lead acid batteries, the kind that have been around for a century. AGMs on the other hand can function as deep cycle or starting batteries, but are 2-3 times more expensive than FLAs.

So if you need to replace your house batteries, switch to golf cart ones.

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Old 09-26-2019, 12:37 PM   #11
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That is what I did. But as was discussed in another thread, those L16s are pretty heavy. GC2 batteries are a lot easier to move around.
Yeah, my L16 AGMs are about 120 lbs each. And they're basically down in a hole. At least they've got good handles and there's plenty of room to stand and move around in front of them with a hatch opened, so it's not too hard to get them out of their spot and basically hand them up to another person in the cabin.
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Old 09-26-2019, 02:07 PM   #12
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Purists will disagree, but I suspect that mixing battery sizes is no problem.

If my reading on this subject is of any value, mixing different types of batteries (not the Ah capacity) is the issue to avoid. The acceptance rate for the recharging current is specific to each battery design (plate thickness, composition, configuration, separation distance, etc.) Different battery types in the same bank will accept the recharging current at different rates, leaving one battery type chronically overcharged, and the other chronically undercharged, leading to premature failure of both types in the same bank (for different causes).


When replacing a bank, it is safest to assume that different battery manufacturers/makes/models/types are all different enough inside that their recharging rates are not the same, and should not be mixed in the same bank.
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Old 09-26-2019, 02:12 PM   #13
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IS there a chance that the 2 x group 24's are a different bank than the 2 x group 27's?

Is there a chance that one bank is the starting bank and one is the house bank? The wording of the OP makes it sound like there is a single bank with 4 batteries configured asymmetrically.
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Old 09-26-2019, 05:11 PM   #14
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IS there a chance that the 2 x group 24's are a different bank than the 2 x group 27's?

Is there a chance that one bank is the starting bank and one is the house bank? The wording of the OP makes it sound like there is a single bank with 4 batteries configured asymmetrically.

Good question.
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Old 09-27-2019, 07:41 AM   #15
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All of the above applies to FLA- flooded lead acid batteries, the kind that have been around for a century. AGMs on the other hand can function as deep cycle or starting batteries, but are 2-3 times more expensive than FLAs.

I expect the same distinctions apply to AGMs, but are often obscured by labeling.

Lifeline offers two lines of AGMs batteries, one for deep cycling, one for starting. Odyssey says "deep cycle" a lot, but I think they're generally closer to dual-purpose design. (OTOH, we've gotten really long service from two separate banks of Odysseys in dual-purpose start/house banks.)

Some other brands seem to label AGMs as deep cycle but also the same models as starting or dual-purpose in their listings. (East Penn/Deka has an example in their table.)

I guess the fine print -- tables of predicted lab cycle, etc. -- applies.

A couple years ago we replaced an aging bank of Odysseys with Lifeline AGM golf cart batteries. The Odysseys were great, but within space constraints I was able to increase our capacity from ~300 Ah to ~440 Ah on that bank by going this route. Not enough time to rate yet, but on paper it seems like the best of both worlds for our particular application... and I do appreciate the "maintenance-free" advantage of AGMs, given access and space issues.

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Old 09-27-2019, 09:31 AM   #16
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I think that the distinctions with FLA deep cycle batteries- thick plates and electrolyte space above and below the plates are probably moot with AGM batteries.


The only AGM manufacturer that makes a distinction between deep vs starting is Optima with their red, blue and yellow top batteries. But the specs show only small differences in CCA and amp hours among the three types. The deep cycle battery is also a little heavier though, reflecting more lead.


Here is an article that discusses these differences- https://www.impactbattery.com/blog/w...top-batteries/



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Old 09-27-2019, 10:27 AM   #17
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I run with 6 GC2s as a house bank (660AH/330AH usable) and a single G31 start battery for starting both of my Perkins 4.236s. When you build up a larger bank, ensure you can charge it sufficiently on shore power and while underway. I upgraded my charger and one alternator to handle the charging duties of the larger bank and a combiner to share the charge as needed.

It all needs to work together in a balanced charging/storage/load distribution system to provide good results. Try to look beyond just the battery sizing when considering electrical system upgrades.
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Old 09-27-2019, 10:30 AM   #18
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Don't forget, a larger bank has some advantages even if you don't really need the capacity. The larger the bank, the less voltage sag you'll see under a given load. If you have high momentary loads, that can be useful even if your power consumption over time is low.
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Old 09-27-2019, 10:41 AM   #19
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......... a larger bank has some advantages even if you don't really need the capacity.
I believe that battery banks are often grossly undersized. To me it's not about whether you believe you need the capacity. The question is, how deep do you draw from the batteries between recharges?

Repeatedly drawing deeply, then recharging shortens the life of the battery IMHO. I'd rather have a large bank that I only dip down 90%, than a small bank that I draw down 50% per charging cycle.

I can get 10+ years out of properly sized Lifeline AGM bank. I have friends that replace their FLA batteries every 3 seasons. These folks also draw then down so far they periodically need to jump the generator off of the starting batteries when the house is dead. (Their genny draws from the house without a dedicated genny start battery).
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Old 09-27-2019, 11:40 AM   #20
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I think that the distinctions with FLA deep cycle batteries- thick plates and electrolyte space above and below the plates are probably moot with AGM batteries.

The only AGM manufacturer that makes a distinction between deep vs starting is

See also Lifeline GPL-31T (deep cycle) and GPL-3100T (start).

https://lifelinebatteries.com/produc...eries/gpl-31t/
https://lifelinebatteries.com/produc...ies/gpl-3100t/

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