Adding second battery

[MPH]

Our fifth wheel trailer only has one battery: an Interstate 12 volt deep cycle marine battery. want to add a second battery. Should I install the exact same battery? Should I just go ahead and replace the existing Interatate and install two new batteries at the same time? Any recommendations on brands?

Thanks!
Melanie

[LJowdy]

It all depends on the age and condition of the existing battery. If the battery is old and tired then buy 2 batteries if it's relatively new and the load test is where it should be then buy 1 battery Always, when adding batteries, make sure the new battery has exactly the same rating as the original.

[JMynes]

If you want to add a second battery it’s best to have a matched pair. So yes, get two new ones.
Rather than marine deep cycle batteries, which are not truly deep cycle, get two 6v deep cycle golf cart batteries and wire them in series. True deep cycle batteries will give you more usable capacity.