One of our two 12 volt batteries failed, same as with our first set. When one goes bad, acid boils over and makes a mess, and of coarse a serious loss of battery reserves. Good practice says to replace both batteries.
With all the discussion on the benefits of 6 volt batteries, I wanted to give them a try. I shopped around and found Sam's club to be a good supplier of 6 volt lead acid and AGM batteries by Duracell. The AGM is twice the cost that of lead acid at $180 per battery, but given my newly created limited access situation, I got the AGM batteries
HERE.
Given all 6 volt batteries are much taller, I had to replace my slide out battery tray with a flat sheet of metal to gain height inside the battery compartment. I found a nice piece of black painted metal being thrown away at work which had a couple of bends that benefited me. I bolted "L" bracket material from a home improvement store to cradle the batteries.
I mounted the brackets to the tray, then the tray to the battery compartment. I then removed the front bracket to slide in the two 6 volt batteries, connected them up nicely, then replaced the front bracket.
Without being able to slide out the batteries, it was difficult to make the connections with a ratcheting box wrench. I used both original short battery cables in between the two batteries for a robust electrical interconnect. As I had originally, the red/+ terminal is on the right side, the black/- terminal on the left side. I used the screw terminals on the batteries to keep the large terminals free to use my secondary battery charger as I like to do at times for quick charging with the generator. Because of the limited access, checking water level is not practical which is why I selected the maintenance free AGM batteries. The next time I disconnect them is when they get replaced.
With the door closed, you can see the front most "L" bracket which is why I painted it black as not to stand out.
I am hopeful that two 6 volt batteries hooked up in series will perform better and last longer than two 12 volt batteries hooked up in parallel.