Dual batteries
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Forum Name: Podmods, Maintenance, Tips and Tricks
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URL: http://www.rpod-owners.com/forum_posts.asp?TID=12713
Printed Date: 24 Jun 2025 at 7:40pm
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Topic: Dual batteries
Posted By: DawgLady
Subject: Dual batteries
Date Posted: 31 Mar 2019 at 10:17am
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When installing dual batteries is it best to have the two connected to each other or have one connected and use the second one as a backup? Thanks ------------- Dawg Lady 2016 R-180 "Lizzy" Georgia |
Replies:
Posted By: john in idaho
Date Posted: 31 Mar 2019 at 10:27am
| If you are talking 6v batteries you will need them hooked up in series. 12 volt doesn't really matter that much but if you do hook two up make sure it is a parallel hookup. |
Posted By: Jholler
Date Posted: 31 Mar 2019 at 2:32pm
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https://www.batterystuff.com/kb/articles/battery-articles/battery-bank-tutorial.html ------------- 2015 rpod 179 2014 Ram ecoDiesel HFE 2009-ish Chihuahua https://ibb.co/S3qvZKG"> 
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Posted By: offgrid
Date Posted: 31 Mar 2019 at 8:41pm
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If you're getting two new batteries then its best practive to get 2 6V batteries and connect them in series. That way both batteries will always be getting or providing the same current so they will stay balanced. But if the batteries are different in capacity or significantly different in age (say more than about a year or so) then its probably best not to connect them in parallel, and instead use them one at a time. They just won't ever get balanced. Be sure to rotate between them though fairly often (say once every few weeks), otherwise the one you're not using won't get charged properly. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: GlueGuy
Date Posted: 01 Apr 2019 at 9:23am
------------- bp 2017 R-Pod 179 Hood River 2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost |
Posted By: offgrid
Date Posted: 01 Apr 2019 at 10:15am
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Sure, I agree, cells do go bad in series strings, and for sure you can't balance a dead cell. End of life failures are inevitable and will always happen in one cell first, and cell shorting is probably the most likely failure event in any PbA battery. But you're still better off having all the cells in series than having a parallel configuration where one string of cells can be cycling a lot more current than another from day one. I've done lots of large battery banks too and at many voltages as high as 240Vdc. You have to have strings of cells in parallel at some point in a large bank. At that point careful design of counductor lengths and connection points to keep the banks at the same voltage and capacity monitoring of each string can help identify problems. In the rpod world its not a problem, we don't ever have banks big enough to require paralleling batteries. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: Happy Tripping
Date Posted: 01 Apr 2019 at 11:36am
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Newbie question - Since we're talking dual batteries here, what is the 'down-side' to using one deep cycle battery until it gets too low for optimal use and then switching it out for a new, fresh, battery? Thanks
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Posted By: offgrid
Date Posted: 01 Apr 2019 at 11:47am
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if say you started with two 12V batteries fully charged, then discharged one to 50% state of charge, then recharged it while you discharged the second battery to 50% SOC, and then repeated that cycle, there wouldn't be much difference at the fairly low discharge rates we have in our trailers. The downside would be that it might be hard in practice to get the first battery recharged right away which would mean that you'd be leaving it at a lower state of charge for longer than if you just connected the two batteries in parallel. Lead acid batteries don't like being left at low SOC for long periods. Then there's the hassle factor in connecting and disconnecting the two batteries to the loads and to whatever you're charging them with. But you could certainly do it the way you're suggesting as long as you kept track of it and got the batteries recharged right away, some folks on the forum do it that way successfully I think. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: GlueGuy
Date Posted: 01 Apr 2019 at 7:45pm
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One option might be to put a separate disconnect on each of two 12V batteries. You could then "swap" batteries by turning one off and the other on. This would still run the risk of having them both connected when they're badly balanced. Probably not a wise plan. ------------- bp 2017 R-Pod 179 Hood River 2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost |
Posted By: offgrid
Date Posted: 01 Apr 2019 at 10:54pm
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There are nice RV/marine battery 1, battery2, both, and off high current rotary switches. I had one my old class a and used it to isolate the engine start battery (1) from the house batteries (2). One of those and some heavy gauge cables would work well as long as there was a way to get the disconnected battery recharged. The problem would be if you forgot and left one battery discharged for a long time. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |