Benefits of the Lithium Iron Phosphate Battery For RVs

An Interview with Garret Towne of AM Solar

Every now and then, a technological breakthrough occurs that has a major impact on the RV industry. One that is creating a lot of buzz and excitement within the boondocking community is the lithium Iron Phosphate (LiFePO4) battery. Why all the buzz? Why all the excitement? We decided to speak with Garret Towne, the president of AM Solar, to learn about the Benefits of the Lithium Iron Phosphate Battery For RVs.

TCA: Thanks, Garret, for taking the time to talk with us. It seems like everyone is talking about lithium batteries now and how their revolutionizing solar power systems for RV’s. Compared to standard wet cell and AGM deep cycle batteries, what makes them so special?

Garret Towne: Lots of things. Lithium batteries are smaller and weigh less, are temperature resistant, provide more usable capacity, provide a higher current output, charge faster, are more efficient, and offer zero voltage sag. They also last longer than standard deep cycle batteries, come with a three-year warranty, require less maintenance, don’t out-gas, don’t require regular full charges, and don’t need to be equalized like standard wet cell batteries.

TCA: When you say that lithium batteries have a “more usable capacity,” what do you mean?

Garret Towne: An AGM battery might be rated for 100 amp hours at 20 hours, which means that if energy is drained steadily over a 20 hour period you can get 100 amp hours out of it. But if you draw all 100 amp hours you will ruin the battery. Typically, you can only get 50 percent of that, so 50 amp hours is all that you should use. But a 100 amp hour lithium battery will let you use up to 90 percent of its capacity without damaging the battery.  Additionally, with lithium batteries it doesn’t matter how quickly energy is drained, which means that they don’t have a time period next to the amp hour rating.

TCA: That sounds like a game changer for off-grid power systems. What do you think is the most important benefit with lithium-ion batteries?

Garret Towne: I think one of the main features RV owners will like is the high rate at which they can absorb current when charging. This means less generator run-time or a quick alternator charge. Other good features include: No Peukert effect (voltage sag), lighter weight, 250 percent more cycles, and low maintenance. 

TCA: Quicker charge times is definitely a big benefit. Being lighter in weight is important, too, especially for truck camper rigs where every pound matters. What is the weight difference between, say, two 6 volt 220 amp hour AGM batteries wired in series and a single 12.8 volt, 200 amp hour lithium battery?

Garret Towne: Two 6 volt 220 amp hour AGM batteries weigh 132.2 pounds, whereas a 200 amp hour lithium battery weighs 92.6 pounds, plus maybe 5 pounds of Battery Management System (BMS) hardware.

TCA: That’s a significant difference in weight. What about safety? Aren’t most of the cell phone fires we hear about in the news caused by lithium batteries?

Garret Towne: There are several types of “lithium” batteries. The LiFePo4 battery chemistry that our systems use is inherently noncombustible. That being said, lithium batteries can put out a lot of current, which could generate a lot of heat in a short circuit situation, like maybe after a violent wreck where your wiring takes a lot of damage. Because of this, we fuse individual batteries in a Victron Lynx Combiner to prevent fires.

TCA: That’s good to hear. Is it true that most lithium batteries operate at 12.8 volts?

Garret Towne: Yes. Lead-acid batteries have a nominal voltage rating of 12 volts and lithium batteries are rated at 12.8 volts. An accurate explanation of what “nominal battery voltage” ratings actually means would require me to review some notes from my college Chemistry classes and the information wouldn’t really be applicable to RV enthusiasts. Anybody who has monitored battery voltages knows that a healthy lead-acid battery operates at a voltage higher than 12 volts. Lithium batteries have a slightly higher voltage than that and typically rest at around 13.4 volts. That being said, when I convert amp-hours to watt-hours for energy storage calculations, I use a factor of 12 for lead-acid and 12.8 for lithium.

TCA: Is it true that the 12.8 volts put out by a lithium battery stays the same regardless of the battery’s state of charge?

Garret Towne: This is mostly true. The voltage of the battery changes very little from about 30 percent to 80 percent. As a result, it’s strongly recommended that you have a shunt based battery monitor when using lithium batteries. The voltage scale you see on some low end charge controllers will be totally useless on a lithium battery bank.

TCA: Most truck campers have battery compartments that can hold only one or two group 27 batteries. What would it cost for a basic 200 amp hour lithium battery system comprised of a single 200 amp hour battery?

Garret Towne: A basic 200 amp hour lithium battery system with a Victron Bluetooth monitor retails for $3,885 and would consist of the following components:

TCA: Cost is the biggest impediment right now for RV owners even with all of the benefits that the Lithium Iron Phosphate Battery provides for RVs. When do you foresee lithium battery prices coming down?

Garret Towne: I don’t foresee prices going down in the near future. The high demand for lithium (not just for RV systems) is actually driving prices up. I think lithium battery prices will stay about the same, but performance of the systems will improve.

TCA: What kind of 110 volt charger is needed to properly charge a lithium battery? Can you use a basic WFCO 45 or 55 amp converter/charger when hooked up to shore power?

Garret Towne: In order to get up to 100 percent you will want to bulk charge lithium batteries up to 14.2 volts, hold them in acceptance for about an hour, then let them float charge at 13.5 volts. You should never equalize them. Most chargers are designed for lead-acid batteries, which operate at a slightly lower voltage, so you won’t get a full charge, but you do get a charge. Some cheap chargers don’t have a float mode, which forces the batteries to stay at a higher voltage, like 13.8 volts instead of 13.5 volts. This isn’t ideal, but it isn’t catastrophic either. If your equipment can’t conform to the ideal charging profile it would be a good idea to eventually upgrade. Victron makes a Phoenix charger that works well with lithium batteries. Victron, Blue Sky and Magnum make solar charge controllers and inverter/chargers that work with lithium. If you want all the features of our V4 lithium control board, you should get all Victron components.

TCA: Unfortunately, the portable charge controller in my Zamp 160 watt Solar Suitcase doesn’t have a LiFePO4 battery setting. If I put lithium batteries in my camper, would I damage them if I connected this charge controller to them?

Garret Towne: AGM battery settings typically have a bulk/absorb voltage about 0.2 volts higher than ideal, but it will work fine with Victron lithium batteries (but may not work with other brands). The problem you may run into has to do with the float voltage being 0.2 volts lower than what we recommend.  At this voltage, no charging will take place during float and you may have to get the batteries pretty low before they get pulled out of float and start to bulk again. So in summary, it won’t damage anything and it should take you up to 100 percent, but after it gets up to 100 percent it might have to be pulled down to about 30 percent before it starts charging again. I’m not familiar enough with Zamp controllers to tell you how their Rebulk works.

TCA: Is it true that lithium batteries can be damaged if you charge them in freezing temperatures?

Garret Towne: Yes, charging a lithium battery at a temperature below freezing can damage it.  Because of this, we have designed what we call a V4 board, which is used in all our lithium systems, that prevents all charging under freezing temperatures.

TCA: This V4 board is part of the Lithium Base Kit you sell, correct?

Garret Towne: Yes, the V4 board is the brain of every lithium system we sell. The V4 board eliminates the need for a complicated network of relays, which actually reduces system cost and complexity.  With the V4 board, there is no need for error prone programming to set up a cold charge disconnect. It is built into the firmware.

TCA: Can you mix and match the size of the lithium batteries used in a rig’s electrical system? For example, can you wire a 90 amp hour lithium battery with, say, a 160 amp hour lithium cell?

Garret Towne: Unfortunately, no. All batteries in a system have to have the same rating; otherwise, the larger batteries will be treated just like the smaller batteries and not use all of their capacity. Keep this in mind if you’re buying a system that you might want to expand upon in the future. It’s going to be a lot easier to add 90 amp hour batteries than it will be to add 300 amp hour batteries.

TCA: That’s good advice for those who have truck camper’s with smaller battery compartments. I noticed that you offer only Victron lithium batteries. Why is that?

Garret Towne: We use Victron because of their reliability and compatibility with other products used in an RV power system. Victron is an established company with a strong supply chain, unlike some competitors we have tried. Victron batteries have internal cell balancing and Bluetooth communication. They can also be configured in systems that shut off charging sources at temperatures below freezing. Additionally Victron’s batteries use only four cells per battery. Some competitors use dozens of tiny cells which may not have the reliability of Victron’s large cells. That being said, we are working on a universal cell balancing board that will work other lithium cells (without an internal BMS) to function in our Victron lithium systems. We expect this product to be ready in the the first quarter of 2018.

TCA: The benefits that the lithium iron phosphate battery provides for RVs is pretty significant. Can somebody who is already knowledgeable with 12 volt systems and RV solar power systems install a lithium battery system?

Garret Towne: We like to think so, but the world is full of surprises. Actually, about half of our lithium systems have been installed by end users. We work closely with all of our customers to ensure a smooth installation and we are continuously improving our documentation. We have never had a customer return a system because it was too complicated, but we have had customers come across some very unique challenges that caused them to bring their rig by our shop for some guidance.

TCA: What percentage of your customers are going with lithium batteries now?

Garret Towne: This is really hard to quantify since we get so many online orders for small parts, but we do about one lithium job per week in our shop and we do about four jobs per week.  We sell several lithium systems per week to DIY customers and outside dealers/installers.

TCA: We really enjoyed talking with you about the benefits of the lithium iron phosphate battery. If somebody is interested in having AM Solar install this system, who should they contact?

Garret Towne: Contact AM Solar first via our website ( If our schedule is full or we are too far away, we have a network of dealers that might be more available. We regularly have these dealers come to our shop for training sessions and we do our best to keep them updated with the latest technology.

About Mello Mike 894 Articles
Mello Mike is an Arizona native, author, and the founder of Truck Camper Adventure. He's been RV'ing since 2002, is a certified RVIA Level 1 RV Technician, and has restored several Airstream travel trailers. A communications expert and licensed ham radio operator (KK7TCA), he retired from the U.S. Navy in 2004 as a CWO3 after 24 years, holds a BS degree, and now runs Truck Camper Adventure full-time. He also does some RV consulting, repairs, and inspections on the side. He currently rolls in a 4WD Ram 3500 outfitted with a SherpTek truck bed with a Bundutec Roadrunner mounted on top.

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