Motorhome Battery Upgrade

Photo of motorhome batteries to illustrate battery upgrade article

Lifeline offers AGM models for house- and starting-power needs

Although it is unpopular, battery maintenance is a necessary part of motorhome ownership and something that is required to keep a motorhome and its systems functioning correctly. After all, monitoring motorhome batteries and ensuring they are adequately charged and filled with distilled water is not a task that most owners enjoy.
In the past, most motorhomes came from the factory with 12-volt starting batteries (usually one or two) that are typically gel or sealed flooded lead-acid (FLA) batteries. For the house batteries, banks were usually comprised of two, four, six or even eight 6-volt FLA batteries.

Battery Wiring Explained

Following are examples of common wiring methods to get the most out of your motorhome’s battery systems.


Illustration of batteries wired in parallelTo increase capacity but not voltage, connect the positive terminal from one battery to the positive terminal of another battery, and the negative terminal to the negative terminal.

Batteries Two 12-volt/80 amp-hours
Total Voltage 12 volts
Total Capacity 160 amp-hours


Illustration of batteries wired in seriesTo increase voltage but not capacity, connect the positive terminal from one battery to the negative terminal of another battery.

Batteries Two 6-volt/200 amp-hours
Total Voltage 12 volts
Total Capacity 200 amp-hours


Illustration of batteries wired in series-parallelTo increase voltage and capacity, connect two batteries in series and two batteries in parallel.

Batteries Four 6-volt/200 amp-hours
Total Voltage 12 volts
Total Capacity 400 amp-hours

Keep in Mind

Parallel combines amps, not voltage.

Series combines voltage, not amps.
Series/parallel combines voltage and amps.

There are many reasons for the widespread use of 6-volt FLA batteries in motorhomes. They have a low initial cost (because of their use in golf carts), they allow for a long life in deep-cycle applications, they tolerate high-discharge applications well, and they can be maintained inexpensively by the addition of distilled water.

But, the drawbacks of FLA batteries are numerous as well. The first issue is the constant need for “watering,” which is checking and refilling of the cells with distilled water. These 6-volt FLA batteries are also prone to corrosion in the battery bay; they require an upright mounting position in a vented cabinet and they self-discharge at a high rate, which means they must be conditioned properly. For example, an FLA battery can discharge 5-10% a month as opposed to absorbed glass mat (AGM) batteries’ low rate of 1-3% a month. Other problems with lead-acid batteries include safety because of the potential exposure to battery acid when refilling. FLAs are also subject to acid leaking when overcharged and must be isolated from electrical equipment due to flammability concerns from off-gassing.

A recent trend has been to replace both the house and starting batteries with AGM batteries, which eliminates the arduous task of maintaining the old-style FLA 6-volt batteries. AGM cells utilize a fiberglass mat or pad that absorbs the electrolyte, which means there is no chance of spilling, which allows for placement in odd positions (basically anything but upside down). Another big advantage of AGM batteries is the lack of corrosion — and they are much less prone to sulfation. Plus, they can be charged more quickly due to their lower internal resistance. While 6-volt FLA batteries are easily frozen if left uncharged, AGM batteries are not prone to this common problem, and they are much more vibration-resistant. AGM batteries perform best when only allowed to discharge down to about 50% of their capacity, which is about 12 volts, so those who boondock need to make sure they keep that in mind when setting up the inverter or autostart generator, and an adequate charging system.

After careful consideration of the strengths and weaknesses of various battery types, we decided that life without battery watering would be very appealing, so we started shopping for new 12-volt AGM starting batteries and 6-volt deep-cycle AGM batteries for the house. There are several brands of AGMs on the market, but after some research and discussions with the experts, we turned to Lifeline.

Lifeline batteries are well-reviewed and a market leader among RV owners, and they are also used extensively by the U.S. Army, Navy, Marines and Coast Guard, as well as the FBI, CIA and the U.S. Border Patrol. Another important part of our decision is that Tiffin (the manufacturer of the Phaeton motorhome we used for this install) even offers Lifeline AGM batteries as an upgrade direct from the factory. If they meet the stringent requirements of an OEM, that means they must work well.

Lifeline AGM batteries have several interesting features. First, they all have lifting handles. If you have ever installed batteries in a motorhome, you know that moving them in and out can be a difficult task. With built-in rope handles, this task is much easier. The next thing we noted is their universal battery terminals. Not only are the terminals lead-free, they are made of a highly conductive copper alloy, and they include all the bolts and washers (also copper alloy) needed for connecting cables. These copper-alloy terminals and fasteners are corrosion-resistant and offer low electrical resistance for maximum conductivity. Lifeline also uses much thicker grids than most AGM manufacturers (1.0 inch versus .050 inch) for longer life, and they use a thick and strong battery case to ensure it stays straight and supports the panels inside the battery.

AGM batteries require a slightly different charging profile compared to most 6-volt FLA batteries, but nearly all modern inverters (and many converters in motorhomes without an inverter) installed on motorhomes have a setting to properly charge them so that shouldn’t be a problem for most owners. The 12-volt AGM starting batteries are usually charged by a 120-volt AC trickle charger when in storage, so even if yours is not currently compatible, they are inexpensive and easily changed, if needed. The Tiffin Phaeton 36QSH used for this upfit was already converted to an AMP-L-START charger several years ago, and it is fully compatible with AGM batteries.

The Phaeton had two Group 31 starting batteries, so we selected the Lifeline GPL-3100T (average online price: $361.20 each) for replacement. It offers 950 cold cranking amps (when tested to IAW battery council standards) at 32 degrees Fahrenheit, and like all Lifeline batteries, is built to aircraft standards. Not only is this battery made in the USA, it also offers an impressive five-year warranty, and since it has the same footprint as the previous batteries in the Phaeton, it was a perfect fit.

For the house batteries, four Lifeline GPL-4CT batteries (average online price: $358.75 each) were installed. The GPL-4CT is a deep-cycle AGM battery offering 220 amp-hours (AH) at 20HR rate, so with four of them wired in series/parallel a 440AH capacity is achieved with all the advantages of an AGM battery.

While the installation is not difficult, keep in mind that these batteries are heavy and lifting them out and installing new ones is a challenge if working solo. Also, there are several safety precautions to be aware of before starting the installation. Since you will be potentially working with battery acid, safety goggles and nitrile-coated work gloves should be worn.

Another caution revolves around the proper choice of tools. Using short wrenches prevents them from touching two different terminals and creating a short. Another option is to use electrical tape around the unused end of the wrench. Since a battery can’t be turned off, not much can be done to render the terminals safe, but there are precautions to help prevent shorting any terminals. When performing this work, it is best not to wear any jewelry, including metal rings or necklaces that could come in contact with the battery terminals. Also, make sure your sleeves do not have any metal zippers or snaps that are conductive.

Before working in the battery bay, make sure to disconnect the coach from any source of external power. This means unplugging from shorepower, turning off the generator and making sure it is not in auto-start mode, turning off the disconnect switches between the batteries and the coach and turning off the inverter. Solar panels must be disconnected from the batteries, using the provided switch in the system. Even if your solar panels do not have a disconnect switch, they will have an in-line fuse that can be removed.
The tools required for this project include basic wrenches/sockets to remove the batteries and the brackets that hold them in place as well as a cordless drill. You will also need sandpaper and paint to remove any existing corrosion from the metal brackets attached to the batteries. A wire brush can be used clean the terminals before installing them on the new batteries. Another handy item is a voltmeter. It’s also best to have a notebook and pen handy to sketch the current wiring of the motorhome’s batteries, or shoot a cellphone photo; doing this will make installation with the correct wiring a breeze. Following is a step-by-step look at installing new AGM batteries:



  1. Don,
    I enjoyed your article on the Lifeline batteries. One of your comparisons with grid thickness states the grid is 1″ thick for the Lifeline battery. I believe it should be 0.1″.

  2. Very nice article on batteries. I live in my coach full time and am currently having issues with my breakers tripping. I do however have a mechanic that is assisting me. Thanks again

  3. I will wait for GOOD lithium type batteries that are affordable. My FLAs last about 13 years! Not a full timer. Trickle charged by a large solar panel.

  4. We replaced the FLAs with AGMs from FullRiver. Same ISO application standards as Lifeline at a significant price savings. Our battery compartment was big enough to up size to L-16 which effectively doubled our storage capacity with the samr footprint.

  5. Another way to avoid shorting issues when working on batteries is to use sockets and a driver with a composite handle. I was able to find them in multiple sizes at Harbor Freight.

  6. My 2016 Thor Windsport came with two 12 V house batteries connected in parallel. Is this correct or should my motor home have had four 6 V house batteries connected in series/parallel to give it more amp hours to run on??? Also would I accomplish enough amp hours to run the motor home on by adding an additional 12 V battery to the two that I already have installed? (if another 12 V will fit)


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