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.