Can one lithium battery replace four lead-acid batteries? In my case, yes, I did exactly that. My one lithium battery does everything that the lead batteries did. My one twenty-two-pound lithium battery replaced my previous four hundred and sixty pounds of lead-acid batteries.
I didn’t start out with the intent to replace my lead-acid batteries but when we investigated the issues associated with four hundred and sixty pounds of extra weight then I made the decision and did just that. I put one lithium battery to the test and it worked and continues to work just fine. At this point, I need to comment that I didn’t know if this was going to work, but it did. This article will explain how it works and what are the limitations of my setup.
Table of Contents
Lithium and lead-acid batteries mixed
I have been operating 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 became difficult to obtain.
“Everyone,” said that it was impossible to combine a lithium battery system and a lead-acid battery system together. 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 how to combine the lithium battery system with the lead-acid system. Both lithium and lead-acid batteries have unique charging needs. You can’t just lump the lithium and lead-acid batteries into one battery bank. Instead, you need to 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 were tasked with operating 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 install, 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. Over the course of that first year, I made frequent measurements of my battery usage 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 estimate 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 and it was 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 that the previous lead-acid battery bank provided. I put the word new in quotes because it really 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 took one of my main battery bank batteries out of my 900 amp hour battery bank 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 effective capacity from 1200 amp hours down to 900 amp hours. Overall this is a 25% reduction in battery capacity. So far, I haven’t missed the extra capacity but I do have to 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 in the process of 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 the only time I have tilted them was for maintenance on the RV roof. Here is a link to our installation. Zamp Obsidian Solar
I had some initial negative feedback on our system design, some people 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 and it is functioning the same 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 an unusually cold 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 during the night and the following morning. From sunset to sunrise we used about 40% of our battery capacity. 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. If you didn’t read the article on that subject, now would be a good time. Here is the link to my article covering that issue. RV Battery Monitor
Morning rain and snow
Then just after sunrise, it started raining and snowing. During the morning, even with overcast skies the solar was putting out less than 100 watts of electricity but our consumption eagerly devoured all the production and depleted our batteries even further.
Recharging started at noon
At noon, our battery bank was down 450 amp-hours 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, 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 made the battery swap after our visit to Henderson’s. The hardest part was lifting the ninety-pound lead-acid batteries. Once they were out of the way, all I had to do is hook up the lithium battery to the already 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 completely 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, even when we are driving between campsites, my main battery bank is almost always fully charged. My backup lithium battery operating my DC electrical system is always charged to 13.8 volts and this is 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 completely deplete my main battery bank.
Backup Battery
My single lithium battery operates like a backup battery except that 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. This means that my inverter has stopped producing electricity and my refrigerator is no longer being cooled.
When that happens, it doesn’t mean that my main batteries are 100% dead, but rather that they are not powering my inverter. The remaining juice in my main battery bank will still be charging my backup lithium battery and it 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. Then and 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 hardest 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 in that it allows discharging at a 150 amp rate, whereas the main battery bank batteries allow 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 the job quite well. Of course, this is my experience and it is because I wired my system expecting that this might be necessary.
The reason I didn’t have to add an additional battery is that I was ready for this to happen and expected to do it sometime in the future. I knew that 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 my fully functional lead-acid batteries away all because of weight concerns. I am relieved this worked so well.
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RV Air Conditioning On Batteries
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!