AGM Coach Battery Issues - Do It Yourself Solar Charging

This post looks at achieving the maximum life and performance from AGM batteries and also the steps an owner who doesn't have access to 24/7 120V charging power can take to keep the batteries in his/her "motor home" at full charge. It includes some of the background information I used to decide on solar power for charging batteries, and it includes a short video.

The Problem
Many motor homes and camper vans include coach batteries. Depending upon how many batteries are included and their capacity, they can be used for powering many things. Typical uses include the water pump, interior and exterior lighting, the refrigerator and small appliances via an inverter. Some motor homes include solar panels for recharging of these batteries. Some do not.

Absorbent Glass Matt batteries, or AGM batteries are very different from the old lead-acid and gelled electrolyte batteries. AGM batteries have a thin fiberglass mat or screen between the lead plates. The fiberglass mat is saturated with acid and is compressed and sandwiched between the plates. This tight packing makes the interior components tolerant of vibration. They are ideal for use in moving vehicles.  Many AGM batteries include bolt-on terminals which are reputed to give a more reliable connection.

AGM batteries are not cheap, but the best ones can last longer than other, less costly batteries. Perhaps 5 to 8 years if given proper attention.

As with all things, there are pros and cons. This post will look into some of these. Part 2 will delve more deeply into batteries. This post addresses the need to keep AGM batteries fully charged.

AGM - Are all Deep Cycle?
Not all AGM batteries are alike. Some are designed to be what is called a "deep cycle" battery and others are not.  So what is a "deep cycle" battery? Such a battery is designed to be discharged and recharged many times. "Deep Cycle" means the battery can be discharged to a lower level of peak capacity and recover. Some manufacturer's state that a deep cycle battery will last three to four times longer than a starting battery under the same conditions.

The batteries I am concerned about are deep cycle batteries.

Advantages of AGM Deep Cycle Batteries
If properly maintained, these are some of the advantages of these batteries:

• Improved resistance to shock and vibration
• Totally sealed
• Reliable
• No acid fumes
• No spilled acid
• No need to add water
• If fully charged can tolerate freezing temperatures (temperatures as low as -40F, but check with your battery manufacturer)
• Longer life as compared to a starting battery

How Do I Maintain a Deep Cycle AGM Battery?
That's a good question and as these are expensive batteries they do need to be properly maintained to achieve their full design life. These are sealed batteries so there is no water to add. Does that mean that the battery is "maintenance free?" No, it does not.

So what do I have to do? Most important is to keep these batteries properly charged! For motor homes or campers which are plugged in each day, this should be rather easy because these vehicles include chargers powered by the 120V shore power. Some vehicles charge the coach batteries when the vehicle engine is running. Others include solar charging systems. Some vehicles include all of the above and a gasoline or propane generator which can also recharge the batteries! However, sulfation remains a problem in lead-acid batteries. More on that later.

The two things to do to achieve long life from AGM deep cycle batteries are:

1. Recharge daily to a full charge.
2. Don't discharge too low. Don't fully discharge.

Is AGM Battery Maintenance Important?
Yes it is. Roadtrek has this statement in the current 210P manual:

AGM Battery Warranty Batteries are warranted by the battery manufacturer for one year from the "In Service Date" of the Roadtrek. 

1. Warranty is voided if AGM batteries are tampered with, topped off with distilled water or allowed to sulfate or freeze due to lack of charge. 

So there you have it. Owners must keep their coach batteries charged. Roadtrek has specific instructions about this for dealers, too. Here's two photos showing the stickers on a 2013 210P. The notice about the "Deep Cycle Gel Battery" is specific (this Roadtrek did have AGM batteries):

Charging AGM Batteries When Storing the Motor Home
For anyone who stores their motor home for long periods of time, there are only three ways to get the power necessary to charge the batteries:

1. Shore Power - 120V plug-in connection.
2. Solar Power.
3. Frequent vehicle or generator use. 

However, not all storage facilities include the necessary 120V power for charging, and not all motor homes include a solar power charging system. If you are like many who store their motor homes, you may not start and use the vehicle for two, four or more weeks. Is this a problem? Yes it is. So what to do? One possibility is to remove the batteries and charge them in your garage. However, that might not be easy as these weigh about 70 lbs. each. I decided the most effective method to allow storing the vehicle outdoors with the batteries inside was to install a solar panel and a solar battery charger. That's what I did, and I place the solar panel inside the vehicle when in use for charging. No rooftop installation required! A video is included in this post.

Solar Power Charger and Sulfation
When the batteries are not being drained by daily use, it's possible to keep them charged if there is sufficient solar energy (daylight) available. For anyone who only has access to solar energy during vehicle storage, this might be the only way for daily recharging.

Will using solar energy and a charger avoid sulfation and are there other issues? In a later post I'll give a more thorough description of what sulfation is. For now, suffice it to say that during battery discharge sulfate molecules (SO4) move from the battery acid (electrolyte) to a lead plate to form crystals of lead sulfate (PbSO4). This is called "sulfation." This interferes with the ability of the battery to perform. It reduces battery capacity, which is simply stated the amount of power a battery can provide. Less power means you run out of power for your camper van electrical devices sooner than expected.

A second problem is as the battery discharges the acid concentration decreases and the electrolyte changes slowly to water. This makes the battery electrolyte more susceptible to freezing. Freezing can damage the battery. Uh, Oh!

What Type of Solar Controller-Charger?
I decided to purchase a controller which the manufacturer states has the following features:

• Full-time automatic battery desulphation
• Uses US Patented pulse battery desulfation technology
• One year unconditional money back warranty and five year "no hassle" warranty on parts & labor
• Plug and run operation - fully automatic easy efficient operation
• Never over-charges - you can keep it plugged in for weeks, months, even a year 
• Temperature compensation - prevents over and under charging from freezing to 130 degrees
• Solar battery charger maximizes battery life and capacity and reconditions weak batteries. Maintains up to 2 batteries at a time. Short circuit, spark and polarity protection. 
• When used as a maintainer....is guaranteed to maximize your battery's life and storage capacity. 

Installation Issues
Finding a convenient place to install the controller and near the batteries can be challenging. The charger manufacturer states "....it is important the controller be in the same general temperature environment as the battery(s)." The temperature sensor lead length is not to be altered and that placed a further restriction. I decided I didn't want  a rooftop mounting of the solar panels at this time. I concluded that a larger wattage solar panel could be put on the dash to charge the batteries via a solar controller-charger. I decided on a 50 watt panel because this would provide sufficient power under lower light and reduced daylight hours, such as in winter or with the windshield not clean. It would allow the controller to charge the batteries even on overcast days. I also wanted simplified controller mounting and wiring.

The manufacturer of the charger-controller says this about mounting the solar controller-charger:

IMPORTANT INFORMATION ON USING PRODUCT OUTDOORS: Weather-tight enclosure. Always mount units in vertical position with cord sets exiting downward to ensure weather tight integrity. Unit must be mounted this way to ensure long term trouble-free life including weatherproof integrity. Mounting in any other manner or using unmounted (parallel to ground) except indoors may cause unit to fail due to water intrusion that is unable to drain correctly to avoid damage. 

Installing a Solar Charging System
So how to go about this? Three things are necesary:

1. Solar Panel
2. Solar Controller - Charger
3. Interconnecting cables

Here is a photo of the battery compartment of a Roadtrek 210P, model year 2013. It shows two AGM batteries. As you can see the battery compartment is very tight:

Here's a brief video of the installation of a Solar Battery Condition Charger and Controller with a 50-Watt solar panel: