Is an AGM or lithium battery in your future?

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By Greg Illes

If you thought you knew a lot about batteries, be prepared to go back to school in the near future: The world is changing.

Once upon a time, RV batteries came from familiar factory names such as Lifeline, Trojan, Interstate, and the like. They were 12V, or better yet 6V “golf cart” styles, made with 19th-century lead-acid technology. They had a great deal of energy storage, considerable weight, and some obnoxious idiosyncrasies associated with their chemical technology.

Around 1980, AGM batteries (Absorbed Glass Mat) were developed, initially for aviation and military use. Still of lead-acid construction, AGM soaked up the acid in a fiberglass mat. Then the whole affair was sealed up tight. Presto, no more leakage, no more water maintenance, no more dry cells. Still pretty heavy, and a bit less energy storage per pound.

Sitting on the sidelines, gel cells and variations on sealed lead-acid were lesser players in the battery market.

Then, electric cars started to become a reality. Almost overnight, vehicle battery needs changed from a few hundred amp-hours of capacity to a few thousand amp-hours. Lead batteries having that capacity made up more than half the weight of early electric vehicles. Something else was needed, and lithium was the answer.

But lithium started out with a very black eye. Laptop battery fires poisoned the market’s enthusiasm for years, due to the very real fears of a major vehicle fire. But eventually, a fireproof lithium technology was developed, and today lithium iron phosphate (LFP) is the choice for any kind of vehicle battery.

After studying this field for some time and working my way through wet cells and then AGMs, I recently bought a set of LFP batteries to run in my motorhome. While my “jury is still out” on what constitutes the perfect battery configuration, I’ll summarize what I know for now.

Flooded cell — This is the common wet cell battery that everybody loves and hates. It’s cheap, messy, widely available. They have to be mounted in a well-ventilated area and must be kept right-side-up at all times. They can accept up to about 20 percent of their rated capacity when charging. High discharge rates will quickly drain them and shorten battery life. Normal life span is about 4-5 years or 500-1000 charging cycles.

AGM — About 50 percent more expensive than wet cell, there’s never an acid mess or need to replenish water. They can be mounted in a closed compartment and in any orientation. Charge acceptance, discharge, and life span are like wet cell.

LFP — Nearly four times the cost of wet cell, but life span makes up for it: easily 8-10 years and 3000-5000 charging cycles. Fully sealed, any orientation, and about 1/3 the weight of wet cell or AGM. Perhaps most importantly for RV/solar applications, LFP will accept 3X its capacity in charge rate, which allows use of full solar capacity at all charge levels. They also can be discharged at very high rates without any penalty (I run my microwave on battery power). LFP batteries have been full-custom applications until recently, but there are now drop-in replacement LFP products for lead-acid batteries.

There is a great deal more to say about all these batteries, but space is too limited here. Clearly, AGMs are worth the expense if you want a cleaner, lower-maintenance setup. But LFP batteries are a total game-changer. Lighter, faster, higher charge/discharge rates. And lots more money up front. LFPs aren’t for everybody — but they do have some compelling advantages.

photo: Claus Ableiter / wikimedia

Greg Illes is a retired systems engineer who loves thinking up RV upgrades and modifications. When he’s not working on his motorhome, he’s traveling in it. You can follow his blog at www.divver-city.com/blog.

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Drew
1 year ago

As in most of these articles the “cons” of various battery types is directly related to the care of the batteries. In addition, it’s a good idea to periodically check battery terminal connections…I do this when I add water to my wet-celled batteries. Contrary to whats written in the article, I’ve gotten a year or two more out of a set of two…that’s pretty satisfactory to me. You DO need a special charger for lithiums- not mentioned in the article. This can add up to several hundred dollars in addition to the cost of the batteries. Another point- for me and possibly others, I may not live as long as the batteries and won’t recoup the cost. These lithium batteries do have a place in the rv world, and as mentioned- those who use solar can take particular advantage of their use.

billy bob
4 years ago

There never seems to be accurate information on lithium bats. All hype. Still to early in the science and application beyond hybrid car use. Think about it, at $500 bucks ea. usually with two bats required, It’s not plausible to drop $1,000 IMO.

Dan
4 years ago

But can you tell us when lithium will arrive? I’ve heard promises of lithium for several years, but we are still waiting. Cost may be a factor, but nobody seems to be selling lithium batteries to even know if the market will support this type of battery. I only found one website selling these things and assembly was required. I wasn’t sure if a standard battery charger would work, so I walked away. Please write an outstanding follow-up article and tell us where to buy lithium batteries and what kind of chargers do we use. Thanks

Wolfe
1 year ago
Reply to  Dan

This is a 3yr old article, but as a quick data dump for other readers:

You need a battery with it’s own Battery Management Systems (BMS) to avoid a new charger. Their BMS makes the battery compatible with lead chargers and idiotproof.

Some solar chargers already handle lithium IF SET TO. External lithium chargers are available, too. With those options, $100-300 per 100AH for batteries without built-in BMS, and you have to know more of what you’re doing.

Look at BattleBorn and Renogy for quality drop-in (with BMS) options $500-1000 for 100AH packs. Look at hundreds of brands for unprotected LiFe (LFP) batteries.

Larry Shoup
4 years ago

We have been using AGMs since the coach was new in ’96. this is the 4th set of house batteries and the 5th of chassis batteries. The only problems we’ve had was with the charging rate of a bad converter that cooked one set of house AGMs. Now all the batteries receive their charge only from the solar panels and life s good. I really appreciate not having the mess of regular lead-acid and at this point don’t think I can justify the expense of LI .

Tommy Molnar
4 years ago

Like everything else that is “new and exciting”, I’ll wait patiently on the sidelines and let everyone else do all the hard work of ironing out the “you know they’re out there” bugs. Interesting stuff.