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Battery upgrade in a 1975 Argosy
Sean Harbour
I'm a computer network engineer residing in Portland, OR, along with my beautiful, understanding wife, and our teenage son. We decided to see more of the state via RV, and have been enjoying it ever since. 
By Sean Harbour
Published on 01/27/2008
How to upgrade the battery capacity of a 1975 Argosy.

When we purchased our well used 1975 24' Argosy last year, one of my concerns was the battery system. A previous owner had replaced the original battery with a small automotive battery. Surprisingly, the battery was sufficient to run most accessories for 24 hours, but not much more than that. However, we wanted a little more (Isn't that how it always goes?).

Here's our plan:

1. Upgrade the factory single battery system to a dual battery system.

2. Incorporate a battery isolation switch allow running off of either battery or both batteries, while providing an emergency shutoff switch.

3. Add in a simple battery monitoring system.

Lets get started!

The argosy's original battery and charging system was located in the right rear of the trailer, underneath a raised closet in the bathroom. Careful measurement revealed that the space would accommodate 2 large RV style 12v batteries, in place of the previous single battery. It was probably a factory option.

As the battery access door was only large enough to accommodate one battery, a design was chosen that would allow the first battery to be inserted through the door, then slid 10 inches forward toward the front of the trailer, making room to insert the second battery.

A cardboard template of the available floor area where the batteries would sit was then made slightly over-sized per the original measurements, then carefully trimmed to an exact fit. Due to some good fortune, the finished template was able to be test fitted from inside the trailer via the internal access door under the bathroom closet.

A test fit of two RV style batteries on the finished template showed adequate clearance, with approximately one inch of minimum clearance.

An examination of the floor of the battery compartment revealed a previous repair to replace some rotted flooring under the old battery. The repair was still in good shape, so we proceeded with the upgrade.

A one inch thick piece of quality plywood was obtained that was larger than the template. The piece was carefully cut to match the outside of the cardboard template. A rectangular piece was then removed from the center of the template, matching the footprint of the two RV batteries.

Two heavy duty drawer pulls were purchased, and attached to the piece at the fore and aft positions. These would serve as the attachment points for a heavy duty nylon strap to restrain the batteries from shifting position after installation.

After a few test fits, the finished piece was installed in the trailer using 1 3/4" wood screws, taking care to align with the external battery access door.

A heavy duty dual battery switch was purchased at an RV camping supply store, along with an inexpensive battery voltage monitor, and the extra battery cables needed to wire everything up. A small plastic utility box was located at a home supply store to house the switch and monitor.

The box was installed in the closet above the batteries, next to the existing 120v fuse box, and wired into the batteries.

The finished installation is neat and clean, and greatly extends the running time of the trailer. When in use, the trailer will run off of the number one battery for several days or until 80% is reached on the gauge, at which time the switch is moved to the number two battery for the next few days. If the active battery is accidentally drained too low, the other battery will have plenty of reserve. The 80% number is a balance of reserve power and wear and tear on the battery. Draining the battery lower than 80 percent on a regular basis will significantly shorten the usable life of the battery.

When shore power is restored, the switch is moved to the "Both" position for charging. This system serves well, and gives us some peace of mind that we can manually turn the switch to the off position for storage or in case of an emergency, such as a short circuit.

I'll be updating this article with some pictures and specifications of the system. It was not a particularly difficult project, perhaps a 2 out of 5. In the future, we will be replacing the antiquated charging system, and possibly installing a voltage converter so we can run small 120v appliances while off the grid.

Enjoy your rig, and we hope to see you out there!

The Harbour family