Can one lithium battery replace four lead-acid batteries? In my case, yes, I did precisely that. My one lithium battery does everything that the lead batteries do. My one twenty-two-pound lithium battery replaced my previous four hundred and sixty pounds of lead-acid batteries.
Originally published March 2023, Updated May 2024
I didn’t start out intending to replace my lead-acid batteries. Still, when we investigated the issues associated with four hundred and sixty pounds of extra weight, I decided to do just that. I put one lithium battery to the test, and it worked. It continues to work just fine. At this point, I need to comment that I didn’t know if this would work, but it did. This article will explain how it works and my setup’s limitations.
Table of Contents
Lithium and lead-acid batteries mixed
I have operated a combination lithium and lead acid battery system since May 2020. (It was right after Covid locked down the country.) Thankfully for us, it was before supplies associated with COVID-19 became difficult to obtain.
“Everyone,” said that it was impossible to combine a lithium battery system and a lead-acid battery system. After almost three years of experience, I can tell you that “everyone” was wrong. My combination system worked just fine.
Unique charging needs
The secret is combining the lithium battery system with the lead-acid system. Both lithium and lead-acid batteries have unique charging needs. You can’t lump lithium and lead-acid batteries into one battery bank. Instead, you must have separate battery banks and a separate charging plan. I published my intentions and details in this article. Hybrid Mongrel Battery
In June 2020, I wrote my next article on the subject, describing the installation and my details about how it worked. It was amazing. The entire battery system worked way better than I expected. My main battery bank had nine lithium batteries. To keep the article short (shorter), I hooked the lithium to the inverter and tasked the main lithium battery bank with operating my alternating current part of the RV. These batteries were charged from my inverter/converter. My refrigerator and air conditioners run from my batteries via my inverter.
My four lead-acid batteries operated the direct current part of my RV. These batteries were charged from the lithium bank via a DC-to-DC charger. These batteries operated the lights and propane heaters. You can get a more in-depth review of the results from this article. Massive Electric Bucket
No Solar Yet
After the initial battery change in 2020, I did not charge our batteries from solar. I was still gathering data. I used all the information I gained during the first six months we owned this RV to size our battery bank. Then, after the battery installation, we lived for the next year measuring and using our battery, recharging it from the generator before sizing our solar panels. Here is the link to my article about using our batteries without solar panels to recharge them. Electricity the hard way, without solar
My main battery bank was sized to operate the RV for more than 24 hours without any additional electricity from any external source. I also wanted the main battery bank big enough to run our air conditioner overnight during the hot nights we might encounter. Both of these design goals were accomplished. I frequently measured my battery usage for that first year with my battery monitor. If you don’t have a battery monitor, you are only guessing. I think a battery install without a battery monitor is incomplete. Here is the link to an article covering that issue. RV Battery Monitor
It was an estimate that 900 amp hours of batteries would run our air conditioner overnight during the summer. The forecast proved accurate. I have several articles about air conditioning from my battery bank. Here is a link to one of the articles. RV Air Conditioning On Batteries And Solar
Get the lead out
Last fall, I gave away my four hundred and sixty pounds of fully functional lead-acid AGM batteries and replaced them with one twenty-two-pound lithium battery. I didn’t do this to prove a point but rather because my RV was five hundred pounds heavy on the rear axle. I started this electrical revision after we made some suspension revisions in Grants Pass, Oregon. Here is a link to the story. Get the bounce-out
Back to the subject of electricity
I started this article about our batteries. Everything in it is related. In this case, it was related to our weight. I wanted to describe why I replaced our heavy lead-acid batteries with one twenty-two-pound lithium battery. The question was, how many lithium batteries would I need to make the replacement?
Equal in function
My new backup battery arrangement works great. My backup battery layout is equal in function to my previous four hundred and sixty pounds of lead-acid batteries. My “new” battery is equal in function because it does everything my lead-acid battery bank provided. I put the word new in quotes because it wasn’t new. I have been using this same battery for three years. I transferred the battery from my main battery bank to replace the removed lead-acid batteries.
Not equal in storage capacity
Even though the new arrangement is equal in function, it is not equal in storage. Overall, I reduced my effective electrical storage by 300 amp hours. This is because I removed one of my batteries from the main battery bank (900 amp-hour) and repurposed it to substitute for the lead-acid batteries. So, I reduced my 900 amp-hour main battery bank to an 800 amp-hour main battery bank.
Removing my lead-acid battery reduced my overall capacity from 1200 amp-hours to 900 amp-hours, a 25% reduction in battery capacity. So far, I haven’t missed the extra capacity, but I must pay more attention to the charge level.
Adding the solar charger
Two years ago, I added solar panels to our system. It has been flawless, with one exception. The salt air in Key West attacked our mounts, creating rust, and I am replacing them one by one. Other than that, everything associated with our solar setup has been hands-off. It requires nearly zero maintenance. I had anticipated needing to clean the solar panels. They have been pretty self-cleaning due to their tilt.
I had also anticipated needing to tilt the solar panels to improve performance. The solar array produces enough power without tilting. So, I have only tilted them for maintenance on the RV roof. Here is a link to our installation. Zamp Obsidian Solar
I received some initial negative feedback on our system design; some thought it was too big. Two observations from this feedback: No one has ever complained that their solar panels recharged their batteries too fast. Two years of performance data identified that the sizing was correct. So here is a link to the discussion two years ago: You have too many solar panels.
Solar tested (again) last week.
Our solar input to the electrical system isn’t new, but it has functioned similarly for the last two years. I sized the solar array to replace all the electricity our RV used in one day—the very next day. Last week, again, I tested it in the winter while camping off-grid in Tucson. How deeply would we discharge our new smaller battery bank?
On a cold, windy night
It was a frigid, windy night with temperatures in the high thirty-degree range, and we were not hooked up to outside electricity. So, we used our propane heaters at night and the following morning. We used about 40% of our battery capacity from sunset to sunrise. At sunrise, we had consumed 360 amp hours of our electricity storage. Much of this consumption was based on running the fans on our propane heaters.
Remember that I measure the energy consumption of the batteries precisely. Now would be a good time if you didn’t read the article on that subject. Here is the link to my article covering that issue. RV Battery Monitor
Morning rain and snow
Just after sunrise, it started raining and snowing. During the morning, even with overcast skies, the solar panels were putting out less than 100 watts of electricity. Still, our consumption eagerly devoured all the production and further depleted our batteries.
Recharging started at noon.
Our battery bank was down 450 amp-hours at noon, and the clouds parted. Half of our storage was gone. Would my solar array be able to replace all the usage? The answer is yes. Our solar array, charging only during the afternoon, replaced all 450-amp hours of drained electricity during the next five hours of direct sunshine on our panels. At six that evening, I checked, and the batteries were back at 100% charge. Given my last two years of monitoring, I wasn’t surprised.
How the battery conversion was made.
One afternoon, I swapped the battery after we visited Henderson’s. The hardest part was lifting the ninety-pound lead-acid batteries. Once they were out of the way, I had to hook up the lithium battery to the existing cables and turn up the charge voltage. There is a small screw on my DC-to-DC converter that turns up the charge voltage. This is the same DC-to-DC converter that charged my lead-acid batteries.
I turned up the DC to DC converter output to 13.8 volts, knowing that I could go higher (up to 14.4 or even 15 volts) if I desired at a later date. This means that I am not entirely recharging my backup lithium battery. If it were a lead-acid battery, this would lead to a short life. The opposite is true with a lithium battery. Operating it at a lower than maximum voltage will lead to a longer life. Here is a link to the Victron website and my DC converter. Victron DC to DC converter
Charging logic and observations about the use
My main bank of lithium batteries is nearly always fully charged unless I am camping without electrical hookups. Because my solar array is ample, my main battery bank is almost always fully charged, even when driving between campsites. My backup lithium battery operating my DC electrical system is always charged to 13.8 volts, about 80% of a full charge.
Whereas my main bank of lithium batteries will deplete when dry camping, this DC battery has priority and remains “fully” charged even when my main battery bank is depleted. Any time any “juice” is taken from the backup battery, it is immediately replaced by my main battery bank. The only time it would start to deplete is if I turned the main DC-to-DC converter off or if I deplete entirely my main battery bank.
Backup Battery
My single lithium battery operates like a backup battery, except I get to use it all the time. If I ever deplete my main battery bank, the backup lithium battery will still be charged.
Here is how my battery system fails (I know this because I tested it): First, if I use all the capacity of my main battery system, I will hit the inverter low-voltage cutoff. My inverter stopped producing electricity, and my refrigerator was off.
When that happens, it doesn’t mean that my main batteries are 100% dead but are not powering my inverter. The remaining juice in my main battery bank will still be charging my backup lithium battery, which will still be at nearly full capacity.
Only after the internal battery monitoring system in my main battery bank individually shuts down each of my eight main lithium batteries will my backup lithium stop charging. Only then will I be depleting the charge in my backup lithium battery. This is how this battery will act as a backup battery to my main battery bank.
Starting the generator
The most demanding job (by far) for my backup lithium battery is to start the generator. Running the lights or fans for the propane furnace is a gradual draw on the battery, but the generator wants lots of juice in a short period. This is why I chose the Lion Energy UT-1300 battery for this task. The Lion Energy UT-1300 battery is unique because it allows discharging at a 150 amp rate, whereas the primary battery bank batteries will enable a discharge rate of 100 amp-hours (each). Here is a link to the battery that we are using. Lion Energy UT-1300 battery
Conclusion
I was prepared to add lithium batteries to my system to make this work, but that wasn’t necessary. My one Lion Energy battery is doing quite well. Of course, this is my experience because I wired my system, expecting this might be necessary.
I didn’t have to add a battery because I was ready for this to happen and expected to do it sometime in the future. I knew my lead-acid batteries wouldn’t last as long as my lithium batteries. When I designed and built the system, I anticipated that I would have to replace the lead-acid batteries, even though I treated them like royalty, never really asking them to do much. I didn’t anticipate giving away my fully functional lead-acid batteries because of weight concerns. I am relieved this worked so well.
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Thanks for including the links to the previous articles. I’m always interested in following the links and getting expanded information on the subject.
My pleasure.
If on a cold day, you used 450 amp hours of electricity in eighteen hours of very little solar but had 900 deliverable amp hours of electricity does that mean that your 900 amp hours of batteries was oversized?
My design was to go for two and half days with no recharge just in case we get a long period of bad weather. Second I want a reserve and not use all the energy. Third I want to be able to run the air conditioner overnight.
Maybe I could have accomplished all the above goals with about six batteries but I think I would hit bottom with only six batteries.
Thanks for sharing, you have the first RV that I have ever heard about that has a backup battery. This is a great idea.
It appeals to me.
Can you estimate how much solar energy you could put out in a single day?
This is a tough question to answer because there are many variables. The post about too many solar panels has lots of detail.
https://foxrvtravel.com/too-many-solar-panels/
Great article, Scott!
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Hi, just wanted. to say that I really enjoyed your article. I’m new to RV living and my greatest concern is being able to stay operational off–grid. Your ideas make it a more manageable job especially the weight difference in the batteries. Thanks and looking forward to reading the rest of your articles!
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