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Old 04-07-2018, 12:37 AM   #1
Join Date: Apr 2015
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Adding second bank of parallel 12 V group 27 batteries

So I finally did the right thing and bought to two 6V 145 amp hour Exide golf cart batteries and really like how much longer they last.

Of course I should’ve just bought exide GC Batteries to begin with, before buying a set of interstate group 27 12 volt batteries that didn’t have much reserve capacity.

Wanted to ask if anyone else has tried to install two separate battery banks into the electrical system of a 2014 FR3 DS 25.

Not sure if you can add battery banks with one set wired in parallel(interstate group 27), and the other wired in series(exide GC 6volt). Want them to be charged by the progressive dynamics converter when it’s connected to a 120 volt source.

I also want to connect my 3000 watt inverter to the 6v GC bank ONLY because GC batteries can be discharged more without damage.


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Old 04-07-2018, 04:10 AM   #2
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All batteries need to be the same type and age. The internal resistance of the batteries is the problem.

"The battery with lower series resistance will take shorter time to charge/discharge as compared to the battery which sees higher series resistance and hence, will experience over charging/over discharging and its life will be reduced."
Quote from my Samalex EVO-2212 Inverter/charger manual. (page 33)

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Old 04-07-2018, 03:07 PM   #3
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In a perfect world, all 4 batteries in two banks would be identical.

Nothing is perfect, so when one battery fails does that require replacement of the 3 batteries that are still working well?

Might there not exist a solution for separate battery banks that compensates for the difference in internal resistance without damage?
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Old 04-07-2018, 03:13 PM   #4
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As mentioned, all batteries should be of same type, age and capacity. By mixing them, one or more will either over charge or undercharge. This will not initially cause a major issue, but over time one battery will fail and could cause the remaining batteries to fail.

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Old 04-08-2018, 01:14 AM   #5
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Adding second bank of parallel 12 V group 27 batteries

Or do two separate banks and use a switch like this

I have two banks one that is for more use and abuse type of rainy nights and one to keep the lights on. If one side gets to low I just flip the switch and am back in action. Also works as my battery disconnect which is way better then the junk that came with the trailer.
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Old 04-08-2018, 03:30 PM   #6
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Bad idea to put different sizes and ages of batteries together. The old ones will pull down your new ones and you'll get way less life. But electrically it will work.
You also have a misconception of 6V vs. 12V deep cycle batteries.
They can both be discharged to the same % full with the same results. Suggested is 50%. Now you may be referring to cycle MANY discharges to 50% you can get and that is SPECIFIC to the mfr. and the battery. I can show you MANY 12V batteries that get MORE cycle life than a cheap 6V.
The reason people like 6v is that they are all DEEP CYCLE and you can buy cheap ones that outperform the CHEAP 12V Dual Purpose models that come with most RV's.
Suggest you give up on the cheap 12Volts and spring for four 6V's ...try Trojans if you don't need to go the Sams club route.
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Old 04-08-2018, 04:04 PM   #7
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Charging Battery

You could use Marine switch to charge une battery bank at a time!
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Old 04-08-2018, 10:31 PM   #8
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You should be fine just don't charge them together and use a switch to charge only one at a time. I had 3 pairs of golf cart batteries with a pair of 12 volt batteries for a couple of years. The extra capacity helped when pulling 1500 watts from the inverter for long periods of time.
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Old 04-13-2018, 03:34 PM   #9
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A simple switch is the answer then.

Thinking to wire the switch to feed 12V house supply on one side, and the other side to a small solar panel battery tender to keep the offline set topped off after being fully charged by PDI converter/charger.

What could possibly go wrong?
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Old 04-14-2018, 06:58 PM   #10
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Battery's & Battery Banks

Curious why group 27's were used vs. group 31's which offer far more capacity in essentially the same package. The replies presented well outline the needs of dealing with differing battery banks. This is not something you can cheat on, that is unless you wish a premature failure.

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