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Open Roads Forum  >  Tech Issues

 > Best practices for dissimilar batteries

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gkainz

Arvada, CO, USA

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Joined: 10/02/2004

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Posted: 09/01/21 03:29pm Link  |  Quote  |  Print  |  Notify Moderator

I got my 2010 5th wheel probably like everyone else - with a single 12V Marine/RV combo battery. I had 2 other nearly new 12V Marine/RV combo batteries from my prior RV that I kept when trading.

I know the drawback of the Marine/RV battery so no discussion needed there - it's what I had and chose to use and they worked well for over 8 years. Not optimal but couldn't have asked much more from them.

Last year 2 of those 12V batteries died. I retired the remaining one to trolling motor duty, and replaced the other 2 with a pair of Costco CG2 6V 210Ah batteries, 200 Watts of solar panel and the Windy Nation P30L charge controller.

Last weekend my batteries didn't make it through the night - still hot summer but at 11,000' the nights get cold and a little heat is nice! So, the only battery available within a hundred miles was another 12v Marine/RV combo battery. I stuck it in the empty box, disconnected the 6V GC batteries and finished the weekend.

I just replaced 1 6V GC battery (the one reading low - the other read 6.4V) and am taking a gamble that 1 year difference may not hurt me (yeah, I know ... Murphy lives at my house and I should have replaced the pair, but Costco's warranty on these is 1 year and I was 13 months ... shake my head).

Anyway, now I have 2 6V GC batteries again in series, and paralleled to the new 12V Marine/RV combo. Charge controller is hooked up across both banks, and house draw draws across both banks.

I just got a Blue Sea 4 position (1, 2, 1+2, Off) battery switch to separate the 2 battery banks (yeah, I know - the 12V battery is not technically a "bank").

Finally, to the original question - best practices on:
- cutting in the battery switch - pos, neg? legs?
- connecting the solar charger to one, other or both battery banks?
- how best to charge one, other or both?

Thanks!
Greg


'07 Ram 2500 CTD 4x4 Quad Cab
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BFL13

Victoria, BC

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Posted: 09/01/21 04:28pm Link  |  Quote  |  Print  |  Notify Moderator

I have mixed 6s and 12s and it worked ok. Trick is to draw from the whole bunch at once while camping and then at home separate them to recharge to full and equalize before banking them all again for their float till next trip.

They have different ways they get to full so that is why to do each type on its own. Use your hydrometer to confirm when each type is full before banking them again for their float.

If you don't float them, you must leave them separate after getting them to full till next time camping.


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CA Traveler

The Western States

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Posted: 09/01/21 05:07pm Link  |  Quote  |  Print  |  Notify Moderator

Once you play the battery mixing game the older batters will drag down the newer one. But you have also mixed types. May/may not be long lasting.

Have all of the batteries load tested and if OK connect them together including solar and the next time one fails replace ALL and stop playing the mixing game.

If you want to play the separate bank game then install a AB switch the positive wires and a AB switch on solar. Or use a AB Off switch. Have fun!


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Bob


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Posted: 09/01/21 05:11pm Link  |  Quote  |  Print  |  Notify Moderator

I installed a full disconnect switch on the negative post for the very same reason that disconnecting the negative battery cable first is a good safety practice.

This is my battery monitor shunt and disconnect switch. While the house batteries are AGM (with no corroding fumes) there are nearby flooded starting batteries. I spray the shunt and the connections with a battery protector.
[image]

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