Originally Posted by RV-burrito
Assuming your first battery is 12 volts and you are intending to keep it at 12 volts you will be wiring the batteries in parallel: positive on batt1 to positive on batt2 to the trailer and negative on batt1 to negative on batt2 to the trailer. That will maintain 12 volts but double the Ah rating.
Searching "12 volt batteries in parallel" in a search engine will give you a good diagram if you need a visual.
Have a great day!
No.other changes necessary if following these directions. Just be sure to use the same qauge wire as the original when connecting the 2 batteries.
Do not just add another battery to an older battery! If the older one is weak it will cannibalize the new battery shortening it's life considerably, always uses matching batteries of the same age.
Also for a rv be sure they are deep cycle batteries, not the same as you'd use in your truck/car. If there's CCA, CA or MCA numbers listed they are cranking batteries not deep cycle. You need a pair of batteries with the highest aH, amp hours, possible wired parallel.