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Old 04-28-2019, 06:20 PM   #1
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Mixing battery sizes

My 93 has 2 battery trays up front. They will fit a series 27 but PO put in 2 wet cell series 24s. One of the 24s needed to be replaced so I put in a new 27 marine batt. The other 24 is still good. Other than the reduced amp hours on the remaining 24 is there a downside to having one series 24 and one series 27?
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Old 04-28-2019, 06:26 PM   #2
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Are the batteries in parallel? If so, the ‘new’ one may try to swap current with the ‘old’ one and therefore mess up the new battery.

Parallel 12 volt batteries should be replaced in pairs, same size, same brand, same date code to get best battery life.

Frankly I’m not a fan of paralleled battery setups...
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Old 04-28-2019, 10:43 PM   #3
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Different voltage curves on those batteries means your 27 will always be working harder than your 24. Stick with the same size and same age.
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Old 04-29-2019, 06:28 AM   #4
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It is possible to do it, but only if you are prepared for some advanced battery analytics and ready to do some “active” battery management. Most folks don’t have the knowledge and skills for this complexity. With mismatched batteries in parallel, you will wear out one or both batteries extremely quickly, and you risk running the weaker battery into “reversal”...which is a really good way to have a chemical and energy “unplanned release”.
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Old 04-29-2019, 06:41 AM   #5
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Hi

Simple answer is that compared to a lot of things, basic batteries are cheap. You are better off with a pair of "what's on sale today" than a really good new one parallel with a worn out old one. Indeed, a new pair of good batteries will cost more. The decision of "are they worth it" is very much a "that depends" sort of thing.

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Old 04-29-2019, 07:54 AM   #6
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Lumatic,

One thing you may wish to consider is a 4 position battery isolation switch. It allows you to select either battery separately, both together or neither (for storage). I got mine from West Marine; boaters like to make sure they have one good battery bank. When hooked up to shore power you can have the converter charge both batteries in parallel. While traveling or off the grid I select one battery and run it until it gets to about 12 volts.
Then it is time to switch and plan on my next full service campground.

We can usually go a few days on one battery - more if we are careful. (We don't have an inverter to run 120 volt devices and have converted to LED lighting.) Two mismatched batteries would not be a problem since they never really "see" each other.

Lots of information and advice out there - see what makes sense to you for the way you like to camp.

Good luck,

Whit Nash
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Old 04-29-2019, 09:10 AM   #7
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Not a good idea.
You should always change all batteries in a bank at the same time anyway. Put another 27 of the same type and forget it for a few years (3-5 for Flooded Lead Acid)
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Old 05-06-2019, 07:33 PM   #8
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that is not a good idea. mix and match will cause no end of problems. as well using the same battery , but of different ages will cause you issues.

like CAR Tires, get then all at the same time and type. replace 1 replace them all
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Old 05-07-2019, 07:03 AM   #9
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Quote:
Originally Posted by Lumatic View Post
My 93 has 2 battery trays up front. They will fit a series 27 but PO put in 2 wet cell series 24s. One of the 24s needed to be replaced so I put in a new 27 marine batt. The other 24 is still good. Other than the reduced amp hours on the remaining 24 is there a downside to having one series 24 and one series 27?

Joining the chorus of "not recommended."
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