Changing a Single 12v Battery to Twin 6v Golf Cart Batteries

Our 2005 Niagara came equipped with a single 12v group 24 deep cycle battery.  We wanted to be able to have extended time dry camping and knew that this single battery was not going to supply the juice we needed.  Rather than adding a second battery as we did in our previous 2001 Santa Fe we decided to convert from a single 12v deep cycle battery to two 6v golf cart batteries.  Don't think that this page is going to be all the information you need to know about batteries, I am only going to scratch the surface.  For more information I suggest reading "The 12volt Side of Life" by Mark S. Nemeth.

Lead acid batteries are generally classified by application (what they are used for) and by construction (how they are made). The most common application is automotive in which the battery is used for starting and lighting. Deep cycle is another common application and is usually broken down into specific applications such as RV, golf cart, renewable energy, and marine. The major difference between the two application (automotive/deep cycle) is that a deep cycle battery has the ability to be deeply discharged and charged many times during its life. An automotive battery cannot withstand more than a few deep discharges before failure. 

First you need to understand that 12v DC deep cycle batteries are designated by their "group", meaning the physical size of the case.  The common sizes you will see in RVs from smallest to largest are group 24, group 27 and group 31.  

As you can see from the table above, adding a second 12v battery would still work but it would take up valuable "real estate" on the "A" frame of the trailer that I don't have to spare.

An additional consideration is that golf cart batteries are more of a commercial grade product, while 12 deep cycle batteries are more of a consumer grade product. What does this mean?  The golf cart batteries are built to a higher standard and can stand up to more abuse than it's 12v cousin. 

All photos are thumbnails, click to see an enlarged version

Now, should you decide to make this change understand that you may need a new charger.  As soon as I was done I hooked up my Guest 6a charger (see it below)  to top them off. After about an hour, OK maybe 2 the charger was HOT. Not so hot as to keep me from holding it, but much hotter than I remember. Looking at the Specs on the back it is rated to charge a 125 A/H battery. Well..... the new batteries clock in at around 225 A/H

Now, the chart below is from the Trojan Battery web page. As you can see, in my application fully charged batteries should register 12.73 - 12.74v DC.

State of charge as related to specific gravity and
open circuit voltage

Now, on my first real test of the batteries I went camping  for five nights at a "dry" campground.  I used the batteries for lights, water pump, fans and the furnace for about 1 hour a day.  Here are my readings:

Here you see the golf cart batteries "in use".  On the ground next to them is the original group 24 deep cycle that came with the pop up.  Look close on top of the group 24, for about $10 Peco Campers sells a wiring pigtail that has the Fleetwood connector, a circuit breaker, about 2 feet of wire and the connectors to connect to the battery terminals.  Now when we are dry camping for more than a couple of days I bring this battery as a "backup".  Wit the new wire connected to this battery it is very easy to disconnect the golf cart batteries and connect this battery.

Battery boxes for the T-105s can be a pain in the ....

Marine stores sell several boxes for two T-105 batteries, but they are over $100 each.  After exhaustive searching I found that the standard plastic battery box has a cousin that will fit the T-105.  This box will only hold a single battery, but two boxes for less than $30 (OK, plus shipping)  is my cup of tea.

Product # 13228 GC-2 Battery Box

Note, everything below this point deals with two 12v batteries!

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Adding a Second 12v Battery When You Already Have One

You can add a second battery to your Pop-Up (if it already has one) easily.  Adding a second battery, depending on the size can more than double the "dry camping" time you have available to you.  While it is nice to have two exactly matched batteries (series, age & condition) it is not necessary.

All photos are thumbnails, click to see an enlarged version

In this photo, we are looking down at the "original" group 24 battery that came with our Coleman Santa Fe.  The stock battery tray is installed at the point of the a-frame of the tongue, right over the point the electrical wiring exits the side of the frame member.

A close up photo shows the 12 breaker installed between the batteries and the trailer electrical system.  Always install a fuse or breaker as close to the batteries as possible to avoid damaging your electrical wiring and/or starting a fire if problems should arise.

This second overhead shot shows the original battery (on the left) connected to the new group 27 battery (on the right). I installed a new battery box on the LP Gas tray, having had to move the tank over about 2 inches.   Note the quick disconnect installed on the wires between the two batteries.  If you use such a device, make sure that when disconnected, there are no bare posts or connectors to short out.

Wiring between two 12v DC batteries is simple, positive to positive; negative to negative.  This wiring is called parallel.  Do NOT connect in series unless you are using 6v DC batteries..  

I connected my batteries together with #12 stranded copper wire.

I violate the rule on mis-matched batteries. I carry both a group 24 and a group 27, but only when dry camping. The only way one battery will try to charge the other is if you connect a discharged battery to a charged battery. Just like water seeking it's level, the charged battery will try to charge the weaker one.

I have read almost every battery web site I can find. The only caution about mis-matched batteries I could find dealt with charging them. If you charge them connected together, either the group 27 will not fully charge or the group 24 will over charge. For this reason I charge them individually (not connected together) with a quality charger in the garage before and after every trip. With both at 12.7 volts, connecting them together will not cause a mis-match.

The trickle charge from the tow vehicle is so little I don't worry about it.

When camping at sites with electric, I only connect one battery.

Simple Rules

1. NEVER connect a discharged battery to a charged one.

2. Charge each battery individually using a quality charger, not your pop up converter before your dry camping trip. See the box below for a description of the charger I use.

3. Connect the batteries together in parallel while fully charged and use them together as a "single battery".

4. Charge each battery individually using a quality charger, not your pop up converter after your dry camping trip. Never store a battery in a discharged state.

You want to use a quality 3 stage charger to both charge and maintain your battery (ies).  I have a Guest 6 amp 3 stage  portable charger (model 2606A) which is designed for charging, maintenance and storage.

As I seldom run the batteries too far down, I only needed the 6 amp charger but a 10 amp is available as model 2612ASome of the nice features of this charger are: It is totally waterproof, so no worries if you need to charge in the driveway and a sudden rainstorm comes up. It is reverse polarity protected in case you hook it up backwards You can check out this charger and other products at the Marinco/Guest Webpage

Caution

As most Pop Up manufacturers place both the LP Gas tank and the 12v battery in proximity to each other on the trailer tongue care should be used in any situation in which the battery may "spark".  This could include connecting/disconnecting the battery wires as well as connecting an external battery charging source.  If there is any chance of LP Gas vapor (did you just change the tank and some gas vented?) being present DO NOT do anything that may cause a spark until the gas has had time to dissipate.

 The main reason for the quick connect between the batteries is to allow removal of 1 battery and installation of a second LP gas tank for fall/winter camping.

If need be, you can charge the batteries while dry camping.  Take a look at my charge cable page.