Current Project - Adding a DC Voltmeter-Wattmeter

Updated August 4
I completed the install yesterday. I did install a fuse at the coach batteries. I'll post a more complete blog in the future on the details of the install. The meter works well. I set the low voltage alarm at 12.1V (about 50% depth of discharge, or DoD). The meter is very accurate. I measured the voltage at the coach batteries and compared to the display. I also measured the mV at the shunt and compared to the ammeter display (has a 75mV shunt). After charging the coach batteries I killed the AC to the coach and with the meter powered, the fantastic fan at speed 1 and an overhead fluorescent on, this was the display. The battery voltage is high because it has some surface charge:

Voltmeter-ammeter-wattmeter with voltage alarm

Updated August 1

Meter in Case, with DC power "Off-On" switch

Making progress. The cabling is in, the shunt is mounted, and I've wired the meter case. I should complete in another hour or so. However, today (August 1) it was overcast and so I worked on the travel trailer; I'm using Meguiar's® Fiberglass Oxidation Remover on the cap. Got about 70% complete before the rain came in. I'll be working on that for another couple of days, weather permitting. Can't do this in the sunlight, or the rain. After completing with the Remover I'll be using No. 45 Polish followed by No. 56 Pure Wax.

Today I wired the meter case, and assembled jumper cabling to extend from the coach batteries to the cable run to the meter.



Original Post, July 28, 2017:
Current project is to put a decent DC electrical meter into the 210P, to monitor the coach batteries.

The 4-LEDS (L-F-G-C) or "Low-Fair-Good-Charging" indicate G "good" at 11.95V, which is not good IMHO. I really don't know the point at which the G indicator goes out, and the F "fair" indicator is illuminated. I don't think I want to find out.

Why my concern? The 11.95V which the LED "G" indicates "good" charge level, is actually a 40% charge level (60% DoD, or "Depth of Discharge") for the AGM coach batteries. Why do I consider that to be a problem? To get best life out of the AGMs it is my understanding that one should not repeatedly discharge below 50%, although these batteries can be discharged 80% (11.66V). The bad news? Doing so repeatedly will shorten the life. How much? As much as 50%, or a 5-8 year battery will make only 2.5-4 years.

So I'm interested in knowing the DoD and a good voltmeter will tell me that. My 210P has the AGM coach batteries, and I replaced the first set a few months ago; they were about 4-1/2 years old.

Is there an alternative approach? I considered just adding meter jacks, but G would have had some difficulty with that, so I'm putting in a digital ammeter-wattmeter. Probably the most difficult was determining how and where to mount it, because routing the cabling is a real pain. After figuring it out I purchased the parts. Should be up and running in a few day, assuming I find some time to complete.

Coach Battery Replacement

My Roadtrek which I could name "Tried and true" or "Rock steady" continues to perform. But there is maintenance to do. Some of this is preventative.

It became apparent that I needed to replace the coach batteries when one of them dropped to 0 volts. It had shorted, I guess, because the bank was at 6.5 volts, which was the voltage across one of the batteries and also the voltage across both. One battery seemed to be doing okay and the other was a tag-along. Just like America, 50% are doing the work and the other 50% is contributing nothing. beyond lip service.

I was aware that the batteries were not able to deliver the designed capacity. Capacity is the ability of a battery to provide the required power (watts) or ampere-hours for the required amount of time. My coach battery capacity prior to the 0 volt failure was below 50%, even though they measured suitable voltage on the indicator in the Roadtrek.

My batteries achieved a life of 4 years. Well maintained AGM batteries can go for 6 years, or more. I use a 50 watt solar panel with de-sulfating controller to maintain the batteries when off of the grid. My measurements indicate this is sufficient when storing the Roadtrek. On a sunny day the batteries will reach peak voltage. After a couple of cloudy days the voltage might decrease to about 80% as an indicator of "state of charge." I take my measurements early in the morning, prior to sunrise and after sufficient time to dissipate any "surface charge."

I'd done a lot of research including opening a discussion via the FMCA Roadtrek International "cyberrally" email.

I'd also designed a LiFePO4 system, should I want to upgrade to a lithium battery system. However, I decided at this time that going with AGM battery replacement was the prudent thing to do. More on that decision in a future post.

I was spending some time in the Tucson AZ area, so I found a distributor who carried the 220Ah 6-volt AGMs I was interested in and would install them for an additional $30. The total price was irresistible.

One thing we observed was the ends of the crimp connectors showed some oxidation. Is that a problem? The oxidation is higher resistance than bright copper, and over time that oxidation will creep up the wire. Resistance is a voltage loss and a source of heat. After cleaning, the ends were again shiny copper.

The installer then applied liquid plastic via a glue gun to seal the end of the connector. This should prevent further oxidation.

The new batteries included lifting means. One of the reasons I didn't do this was the fact that the old batteries didn't have such a means. I was faced with either purchasing a strap, or wrestling with 63 pound batteries. I've stored the lifting means in the compartment with the batteries.

Here's the completed installation:

After several weeks of monitoring the battery voltage, and with the solar panel connected, it seems the new batteries are doing well, achieving maximum terminal voltage and sustaining it into darkness.

My Roadtrek which I could name "Tried and true" or "Rock steady" continues to perform.

AGM Battery Alternatives

It's again that time of year when attention goes toward the coach batteries in the RV. When the RV is in frequent use, this is never an issue. Running the engine will charge those batteries, as will plugging into shore power.

However, in winter, some of us put our RV into storage. Those AGM coach batteries then self-discharge. Sulfation may occur and if the batteries are sufficiently discharged they may freeze and undergo permanent damage. In winter, our attention turns to the coach batteries. When spring arrives some of us may be unhappy to find that our batteries have only 75-85% of rated capacity, or less.

Is There a Better Way?
In my case, I installed a 50 watt solar panel and charging system to help those AGM batteries. I also installed a smaller solar panel to offset parasitic drain for the engine battery. Both of these have seemed to help. I went to the storage facility for my RT and the coach battery monitor indicated my coach batteries were in "fair" condition. That has been typical; I suspect my RV which was purchased one year after manufacture had damaged AGM batteries. My current interest is in getting the maximum benefit from whatever coach battery system I have.

On my most recent RV inspection the engine started fine and I charged the coach batteries for a half-hour. Not a lot, but intended to augment the solar charging system.

But is there really a better way? I think lithium batteries are the way to go. I've begun exploring this.

1. Smaller lithium battery systems have been proven in sailboats.
2. Faster recharge times. 
3. Lithium batteries have half the weight of the AGM batteries on a weight versus output basis; that's another 70 lbs. of gear, or improved fuel economy, in my case. Or more battery capacity at the same weight!
4. Lithium batteries, while more costly initially do have a higher number of charge-discharge cycles and can tolerate deeper discharges. In simple terms, they will last far longer than the AGM batteries. 
5. There is some evidence that lithium batteries cost less over the life of the battery than do AGM batteries. For anyone who intends to use a RV for 10 years or so, this is significant. 
6. Lithium batteries don't freeze at low temperatures and have the winter problems of AGM lead-acid/water batteries. In other words, fewer winter maintenance issues. Roadtrek states in their 2014 210P manual "AGM Battery 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."
7. Lithium batteries have lower self-discharge rates. In other words, they can be stored for extended periods at full charge and don't self deplete. 
8. Lithium batteries can tolerate deeper discharge than can AGM batteries.
9. AGM batteries have high ambient temperature restrictions.  AGM batteries are designed for an average annual temperature of 77F (25C). If the average annual temperature is 95F (35C) then the battery life will be reduced by about 50 percent. 

Improving Solar Response
I've also been researching improved solar panels and I've decided it would be pointless to put them on an AGM battery system.  Improved solar panels would benefit with an improved electrical storage system. In other words, the system is limited by the weakest link in the chain.

I'll continue my research and will post the upgrades as I make them.

Why Do Manufacturers Use AGM Coach Batteries?
That's a question you might ask. The reasons are straightforward.

1. AGM technology is well established and existing system designs are in place.
2. Alternative battery technologies, such as lithium, are at a higher initial cost. This increases the purchase price of the RV.
3. New designs will require engineering manhours which is an additional cost to the RV manufacturer.
4. Other technologies are new and are not well understood. In other words, while technically superior, some technologies have not yet been widely offered because the sales, marketing, management and engineering departments at RV manufacturers have not yet come to grips with the benefits.
5. It's a competitive world. Most users (RV buyers) compare total cost to overall performance. It's only after purchase that the limitations become apparent.
6. Leadership entails risks. However, most western companies are risk-averse. My company recognized this. We were leaders in our field and as president I would remind our employees that "There is the leading edge, and then there is the bleeding edge." I can say that we did find ourselves from time to time on the "bleeding edge." Good engineering, attention to detail and serious prototyping kept us and our clients from going over the edge. I would say that lithium batteries, which are well proven in smaller systems such as sail boats are not at all like what I was facing with hardware and software which didn't perform as expected. This isn't 2008, nor was the microprocessor invented only four years ago. This is 2015 and there are a lot of Tesla motor vehicle on the road, and lithium batteries are not uncommon on sailing vessels. Lithium batteries are entering the mainstream.  

AGM Batteries Sulfation, RV AGM Battery Care and Charging - Part 2

This is part 2 about care of AGM batteries in a "motor home." The previous post is part 1.

After a significant amount of research into the chemistry,  technology and charging of AGM batteries I became concerned about battery damage including sulfation and freezing the battery electrolyte. I want to achieve longer battery life and have 100% rated battery power available when I am off the grid and am not running the generator. I decided I needed to make an improvement and installed a solar panel and solar controller-battery charger for my coach batteries. This post looks more closely at the research that led to my decision. I'll provide in brief the why's, as well as some of the "do's and don'ts." I am not promoting any product here. This describes the issues and the solution I chose, and provides background information about that decision. This may be helpful to others.

I chose a 50 watt solar panel and a "Solar Charger/Maintainer/Desulfator" rated for use with solar systems up to 180 Watts. The solar panel is not used when the vehicle is in motion. I decided on this approach because:

1. The replacement price of the coach batteries would be about $250.00-$400.00
2. The Camper Van may be stored for weeks and sometimes for months
3. It's desired to achieve the maximum life from the coach batteries
4. It's desired to have the batteries provide the maximum rated power throughout their life
5. When stored,  120V shore power is not available. Solar power is the only available power option unless the generator or vehicle motor is running.

The following post provides, in brief, what I have learned on this subject and how what I learned has influenced my decision  Why would I want to do this? I'd like to spare the reader the time to replicate what I have researched.

How to Achieve Full Life and Power from AGM Batteries
That is the goal. Get maximum power and longest life from the AGM coach batteries. Doing so should provide a more pleasurable trekking experience and reduce the annual cost of operating the camper van.

Deep Cycle AGM Batteries require complete charging, but not overcharging to achieve full lifespan, avoid freezing damage and provide the amount of power expected from them.

Roadtrek states in their 2014 210P manual "AGM Battery 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."

Here are the most important things that dictate battery life:

• Preventive maintenance
• Depth-of-Discharge (avoid discharge below 75% charged)
• Charging to a full charge
• Temperature conditions of the batteries (cooler is better). Batteries are designed for an average annual temperature of 77F (25C). If the average annual temperature is 95F (35C) then the battery life will be reduced by about 50 percent. 

What is full life? It varies. 3-5 years is fairly typical according to published information. However, AGM batteries are reputed to achieve up to 10 years if properly maintained, kept cool and if used in such a manner to maximize battery life. I decided I would prefer to replace these batteries every 6-8 years instead of every three years. I also decided I do want the maximum battery power to be available when needed.

Avoiding Sulfation and Extending Battery Life
Sulfation if left unchecked will kill the coach batteries. Sulfation begins when the batteries are not fully charged, and storing them unless "float charged" continues the sulfation process. The RT and most RVs include charging systems for the coach batteries. However, there are periods in which these 120V or engine and generator powered charging systems are not available. That is a problem. So how can I achieve my stated goal of long life at maximum power from these batteries under my actual storage and charging conditions?

Frequent charging while avoiding overcharging of AGM batteries will reduce, but not eliminate sulfation. Sulfation occurs each time a battery is discharged. Storing a battery is reputed to cause self-discharge and sulfation, and this is more serious at higher temperatures, above 75F.  Batteries which are not used weekly may experience sulfation.

Sulfation is the gradual coating of the positive lead plate of the battery with lead sulfate (PbSO4). Simultaneously the battery electrolyte, which is sulfuric acid (H2SO4) on losing SO4 molecules becomes diluted by water. This occurs during battery discharge. The chemistry is oxygen molecules (O2) from the positive lead plate combine with hydrogen molecules (H2) from the battery acid and the result is water (H2O).

Because AGM batteries are chemical devices, cold weather will slow the sulfation process while hot weather speeds it up. In other words, full charging may be more important at higher temperatures. On the other hand, as sulfation occurs battery electrolyte (acid) is diluted by water molecules and will freeze at lower temperatures than the normal electrolyte of a fully charged battery. Such freezing can damage the battery.

Normal charging does not remove all sulfate molecules from the plates. Over time they build up on the plate and ultimately contribute to the demise of the battery. Sulfation, or the formation of lead sulfate can permanently reduce battery capacity. If unchecked it can kill the battery.

Keeping batteries fully charged and reducing sulfation will extend the life of the batteries and provide optimum capacity. Battery life expectancy is directly the result of how well these batteries are maintained and how they are used (or abused). Key points are:

• Don't overcharge.
• Don't undercharge
• Keep fully charged and don't store undercharged.
• Use and keep the batteries at their average design temperature.  
• Apply a periodic full-saturation charge to de-sulfate the batteries.
• Don't over-deplete; reduce the average "depth of discharge." and avoid "deep discharge".
• Reduce the number of "discharge-charge" cycles. 
• Don't charge if over 120F and don't charge if the battery is frozen. 

Some of the above might not be possible. That is why many batteries don't survive for more than 3 years according to some published sources. However, I'm convinced that good care and attention to these details will extend battery life for most users. One manufacturer of battery chargers/maintainers/desulphators claims that certain models of their product "can more than double the useful life of new batteries." I can't verify that. However, it's prudent to ask why some batteries fail within 3 years while others go on for 6 or more years.

It is my understanding there are two types of sulfation: 1) reversible (soft sulfation), and 2) permanent (hard sulfation). Reversible sulfation is normal and can be corrected by a specific charging regimen. When charging, the PbSO4 is converted to lead and the SO4 combines with hydrogen to form electrolyte. Non-reversible sulfation occurs when a battery has been in a discharged condition, or "low state-of-charge" for a longer period, be it weeks or months. In such a state the sulfate crystals become permanent, cannot be reversed by charging methods and the capacity of the battery is permanently reduced and impaired.

Charging and Reducing or Reversing Sulfation
Special charging techniques are reputed to reverse sulfation.  Battery charging states include:

• Bulk (high, constant current)
• Absorption (constant voltage)
• Float (hold at 100% charge)
• Equalization.(controlled absorption overcharge)
• De-sulfation

A microprocessor "smart" charger will include three or four of these states. Special chargers provide a fifth state called "de-sulfation." One charger manufacturer declares "Patented high-frequency pulse desulfation is designed to reverse and eliminate battery sulfation."

There is some controversy about the claims of "reversing sulfation." One critic states "simple, electronic de-sulfation is a one size fits all approach." On the other hand, I've seen no comments or evidence that such pulse desulfation techniques can harm the batteries.

How to Apply a "Full Saturation" Charge
Such a charge is a general recommendation for lead acid batteries. However, some AGM battery manufacturers have specific requirements of this type of charge and if not followed it is possible to damage the batteries. This type of charge is also called an "Equalizing" charge. This is done by a deliberate overcharge of the batteries. The problem with sealed AGM batteries is there is no way to measure the electrolyte condition and so the equalizing charge is guesswork and may be based on terminal voltage. My guess is it's better to use a good 4-stage charger and avoid deep discharges.

Choosing a Battery Charger
The charger included in your RV or camper van is probably a three-stage "smart" charger which includes bulk, absorption and float stages.  "Float" charging is not "trickle" charging; a trickle charger can overcharge batteries!

I decided to add a "Charger/Maintainer/Desulfator" which was designed for use with solar panels. I also selected a solar panel which is overcapacity. This approach compensates for the lowered solar power that is available when daylight is minimized, such as during winter hours or when overcast. It also provides for a higher charging rate when there is optimal sunlight available.

Using a 50 watt solar panel provides a maximum 4.17 amperes of charging current at 12V during peak sunlight conditions. That's more than sufficient for maintaining or topping off the batteries.

Overcharging is to be avoided. I decided to use a solar charger that includes temperature compensation with float charging. The temperature sensor is attached to one of the battery terminals. This permits charging in cold and hot weather. The manufacturer states compensation works over the range 0F to 130F.

The solar charging system is only used when the batteries are not being charged via 120V shore power, generator power or via a running vehicle engine. It is intended to be used at any time the vehicle is stationary. The solar charger is connected directly to the batteries and operates independent of the position of the battery disconnect switch.

How Long Does it Take to Charge the Batteries?
The answer to that question is determined by the amount of sunlight available and the condition of the batteries. The purpose of the solar charger is to take the batteries from a condition of 85% to 90% charged to full charge, or apply a "topping" charge. Once at full charge, the goal is to "float" and desulfate the batteries while avoiding overcharge. Temperature compensation reduces the float charge as the battery temperature increases.

To bring a discharged battery to full charge can take 7 to 10 hours or longer. That is not the purpose of the solar system, but if there is sufficient daylight hours such charging is a possibility.

How Does "Depth of Discharge" Influence Battery Life?
Any AGM battery has a service life which is measured in number of discharges and the "depth of discharge." As a rule of thumb, the less the "depth of discharge" the longer the life of the battery, but it should be discharged to 90% peak when used. In other words, if used the battery should be discharged 10% and  a battery which is repeatedly used and discharged to 50% of its peak capacity and then completely recharged may be usable for 1000 cycles. If one cycle occurs each day, then the battery may have a life of 3 years.

That same battery, if discharged to 75% of its peak capacity each day and then fully recharged may be usable for 2000 cycles. Under such conditions the battery may have a life of 6 years.

Furthermore, that same battery if discharged to 25% of its peak capacity each day and then fully recharged may be usable for 500 cycles. Under such conditions the battery may have a life of only 16 months. Discharging a battery to less than 25% capacity is to be avoided.

What are Battery Storage Choices?
Batteries can be disconnected and then charged if they are not going to be used for long periods of time. It's best to store the battery in a cool or cold place (sulfation is slowed when it is below 75F). Here's a few methods:

1. Turn the battery switch "off" and then connect a 3- or 4- stage microprocessor controlled battery charger and fully charge the battery. If the charger includes an automatic "float" mode it can be left connected to the battery for long periods of time. Check your manufacturer. 
2. If the battery is fully charged connect a "float" charger, again check your manufacturer.
3. Alternately, the battery can be removed in the vehicle and kept above freezing while a float charge is applied. 

Avoiding the Freezing of Batteries
If the electrolyte in a lead acid battery freezes, the battery will probably be damaged. The capacity of such a damaged battery will be reduced. What are the freezing temperatures of a depleted battery? A battery in good condition that is 100% charged has the maximum concentration of sulfuric acid as electrolyte. As the battery discharges, the concentration of the acid is reduced as water molecules replace acid molecules in the electrolyte. Here are typical freezing temperatures for lead acid batteries at different charge states:

100% Charged = (-) 77F, or (-) 67C.
75% Charged = (-) 35F or (-) 37C
50% Charged = (-) 10F or (-) 23C

Other Sources
There are a lot of web based sources on AGM battery maintenance and charging. Enter  "AGM battery maintenance", "AGM battery charging" or "AGM Battery desulfation" in your favorite search engine and you'll get a list.

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: