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Old 11-27-2021, 12:35 PM   #1
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Mixing battery sizes

My house batteries may have reached their end of life, almost 5 years. Still have a few things to check, but the time is coming so I am making plans.

I have 6 ea. 6 volt batteries in a serial-parallel configuration, and am looking to get a bit more battery capacity to (1) run longer without shore or generator power, and (2) allow me to use the full charging capacity of my Magnum inverter-charger.

My two options are to add two more batteries and figure out how to put them into the available space, or to go with larger capacity, physically larger batteries.

My problem is that two of the batteries are mounted in a location with no headroom, where the other four have 12 or so.

Can I put two GC2s in series and 4 GC2Hs or 901 size in the same series-parallel configuration I have now to get the additional capacity?

Thanks in advance,
Dean and Mike
2016 Fleetwood Discovery 40E
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Old 11-27-2021, 12:47 PM   #2
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You should be fine with what you propose. All of the batteries will be new and the same type- FLAs, so they should coexist ok even with different sizes.

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Old 11-27-2021, 12:55 PM   #3
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Another idea: I have 6-6v AGMs in series/parallel. I use this bank for starting and the coach.
'04 Newmar MADP, 1100w of solar, towing a lifted Rubicon
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Old 11-27-2021, 01:40 PM   #4
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Until recently I did not know how important it is to do a equalizing charge especially multiple 6v wet cell batteries. Uses 15.8+volts
1. Mixes up the sulfuric acid and water to prevent stratification. Acid only on bottom.
2. Removes sulfate from plates.
Both improves battery life. I'm on 7 years.
Don't mix different size and type batteries.
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Old 11-27-2021, 02:41 PM   #5
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Every time you drive, or plug in your motorhome, you combine two different size and type battery banks thru your isolation/bridging solenoid.
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Old 11-27-2021, 03:11 PM   #6
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You'll be fine. The only difference between those batteries is amp hour capacity. The charger won't care.
Bob & Barbara
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Old 11-27-2021, 08:38 PM   #7
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I neglected to mention that my plan would be to have all the same battery type FLA or AGM. They will be from the same manufacturer if I can do it.

Thanks for the inputs, including the reminder about equalizer charging. I will give that a shot before I spend money on either approach.

Dean and Mike
2016 Fleetwood Discovery 40E
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Old 11-28-2021, 07:04 AM   #8
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AGM Battery Equalization

Lots of good advice posted.

Don't try equalizing most brands of AGM at 15 volts. They do not have free flowing acid that can be stirred. Most will vent. Lost water cannot be replaced.

Substitute long charging time at 13.6 volts to clean sulfate from the plates. 24 hours can do a lot. Life Line batteries are more robust. See manufactures instructions.
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