If your batteries currently set in a welded angle strip area on top of your Trailer Tongue Area like on mine it is very easy to add a long angle section on the inside of the current angle that is welded to the top of your frame...
I can fit three GP24 12V 85AH Interstate Batteries across my OFF-ROAD trailer tongue. I could very easily add longer right angle metal strip to extend the batteries out over each side of my present mount.
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I originally had four of these GP24 85AH batteries installed here in 2009 using added angle strips and was using a WF-8945 WFCO Converter/Charger at the time and one of my 12V batteries ended up getting a shorted cell due to the boiling out of fluids. The bad battery got very hot to touch when i first noticed it. The WF-8945 converter/charger apparently never would go into its smart mode charging modes and always put out 13.6VDC... I replaced it with a PD-9260C 60AMP DC converter/charger and continued on with the remaining three 12VDC Batteries you see in the above photo. They lasted until the 2016 season and would not hold charge anymore. I check my batteries on a very regular basis now even after they always show fluids at the required levels. All out of habit I reckon...
My camping plan using the three 12VDC batteries was to use them overnight drawing around 25AMPS DC current between 6PM and 11PM each evening which would drop them down to the 50% charge state around 8Am each morning. Then i would re-charge the three batteries to their 90% charge state using my 2KW generator hooked up to the trailer shore power cable. This would take around three hours each morning to get the three batteries back up to their 90% charge state so that I could do all of this all over again for the next day/night off the batteries. I could do a good 10-12 cycles of the the 50% to 90% charge cycles before having to do a full 100% charge cycle and not do any harm to my batteries. Here on the East side of the US you have to pick where you camp as the use of Generators is not always guaranteed. They have generator run time rules it seems. Using you can find it OK to run one between 8Am and 8PM but i never was able to run mine after 8PM anywhere i camped on public places. Even in the Natl Forest areas...
I presently am in the process of using a Torklift Battery box that will be 59-inches long and will sit inside the current angle strip on my trailer tongue area. This will extend out over a foot on each side of my trailer tongue area when installed. This will house 4ea GC2 225AH 6VDC batteries (Planning on the Trojan T-105 but may end up being the CostCo specials depending on the price savings) and having them wired in two series connected groups in parallel will give me 12VDC at 450 AHs capacity to allow me to do some serious camping off grid trips like we love to do...
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We all learn from our mistakes hehe...
Roy Ken