Originally Posted by RichHog
This should be inserted in every Trailer manual that comes with a trailer with "the Switch".
The PO had replaced only one of the factory batteries a few months back, Should the other battery be replaced as it is the weak link in the overall power in the system?
Batteries should always be replaced in pairs (or entire bank, if more) unless all are just a few months old (ie. you got a defective new battery and it failed early in life).
In practice, I'm not sure what I'd do if my other battery was only a year or so old. I would do some extensive testing out of the coach before assuming the replacement and the "slightly used" one were performing differently.
That being said, I think pretty much all the "experts" will tell you to replace all hooked in parallel (12V) or series (6 V) should be changed out together.