Battery ?

When you get everything connected do a complete charge then let them go to float for a day or two. Then check the specific gravity of all the cells and record the results. In the future you can do a quick check on the lowest cell.

How often you have to add distilled water will depend on how hard you run them.

What are you using to charge? You want far better than a 13.6 converter.

phillyg X2 Your new batteries will be drug down to the used battery strength. Not a good idea

Yes. It will be fine. I have four group 27 batteries that are used together. They are 2009, 2012, 2015, 2016 and all love each other and get along just fine. Also have a 2008 that is still working but I now moved it to my trolling motor.

No problem if the originals are in good shape. If you store the RV without power or float charge on the battery it will be better to separate the parallel sets. The additional batteries will be due for replacement when the originals are ready so in effect you will get one less year of service from the added pair.

Can you, yes. Should you, no. Conventional wisdom is batteries should be matched in type AND age.

routemaster wrote:
Can I add same make/model 2 new 6volt golf cart batteries to a year old golf cart battery bank?

Yes....if the current ones are relatively healthy.
The new bank needs to parallel the old one.