Lou @RVHabit

Replacing and Installing AGM 12V Deep Cycle Batteries in the RV

My RV is a Class C and like most Class C's the batteries are located below the entrance steps. As you can see the location held two group 27 flooded lead-acid batteries. The wires are pretty stiff and moving them around to check the fluid levels was quite a task. My quest for replacement was to find the most cost-effective maintenance free deep cycle battery that would fit. Lithium batteries have some great advantages but the cost was too prohibitive.

After months of going back and forth and researching what other RVers have found to work best, I decided on AGM deep cycle batteries. Now each type of battery has their pros and cons but the big pros for me was AGM batteries are maintenance free, slow idle discharge rate and they charge quite fast compared to a typical lead acid battery. AGM and Flooded are both lead acid batteries but without getting technical AGM batteries suspend the electrolyte solution between the battery plates with a special glass mat. This allows for no maintenance.

The first step was to remove the old batteries and clean up the battery box. I measured and with some finagling I figured I could fit and upgrade the size battery to a group 31. The opening dimensions on my steps are 25.50" x 7.25". The box dimension is a little larger at 27.75" x 9.25". Typical AGM group 31 batteries are 13" wide by 6.25" deep and 9.5" high. They do vary a bit depending on brand. Now what brand you purchase is all up to you. I will tell you that most batteries in the United States are made by the same few companies. I chose Duracell because I was able to get them on sale but I have heard good things about Diehard Advanced Gold AGM RV or Vmaxtanks which is available on Amazon. All are in the same price range.

Once I got all the wires off I checked and actually found several loose eye ring connections. I repaired all of them and re-taped the ends. The first battery went in quite easily. In order to get the second battery in I pushed the first battery all the way to one side utilizing the larger box size versus the opening size. The second battery just fit with little room to spare. Once in the box there is plenty of room with over one inch on each side of the battery. I centered the batteries and began the connections.

Since these are 12v batteries the first connection was to connect both batteries in parallel. I connected both positive terminals together then both negative terminals together. This maintained the voltage at 12v but doubled the 105 amp hour rating of each battery to a total bank of 210 amp hours. Although some will say it does not matter, most agree that all the positive connections go to one battery and all the negative connections go the other or last battery in the group. This in theory pulls the power through all the batteries evenly.

On my RV I have four positive connections to be made to the batteries. The coach positive, the converter positive, the voltmeter positive, and the Bigfoot jacks positive. They were all attached to the first battery positive post except the Bigfoot jack's positive wire. The wire did not reach the first post so I attached it to the positive post of the second battery.

The negative voltmeter wire and the negative chassis wire were connected to the negative post to the second battery. The install was straight forward. Labeling the wires, taking a photograph before removing the old batteries, or drawing a diagram helps. I now have maintenance free batteries I can rely on. The upgrade for me was well worth the few extra dollars for AGM versus traditional flooded lead-acid batteries.

Check out my short video below of the install. It shows fitting the batteries in the box and the wiring I did.