Flooded, AGM, Lithium. Which battery is best? Well, we recently tested all of these in laboratory-controlled conditions. We determined the real-life performance and lifetime costs of each to share with you which is the best RV battery out there.
An Unexpected Opportunity
We visited Reno, Nevada where Battle Born Batteries are manufactured. While there we had the opportunity to interview the founders of the company.
The primary purpose of the interview was to discuss a White Paper they had published earlier in the year about cold weather charging lithium-ion batteries. The paper included a bunch of data comparing lead-acid AGM batteries and lithium-ion discharge characteristics in both warm and cold temperatures.
We made a video about this white paper and got lots of feedback. I took the opportunity to ask CEO Dr. Denis Phares and COO Sean Nichols many of the questions that were posed to us.
At one point during the interview, Nichols started talking about battery capacities. He said the lead-acid battery companies have such stringent battery parameters that it’s nearly impossible to get the capacity ratings they tout. He told me that an RVing family will not be able to get 50% of the battery power out of their lead-acid RV batteries like they’ve been told.
Battery Testing Invitation
I questioned this further and asked if I could see the testing setup they used. In response, Nichols offered for me not only to see it but to come and replicate or run my own experiments. We had some more time in the area, so I decided to take him up on this opportunity.
I’m a bit of a nerd, and also an electrical engineer with a background in Power Systems and battery storage systems for both residential and commercial backup power applications. While I have installed many Power Systems, I have not done much load testing on batteries. This seemed like it would be a neat opportunity to find out once and for all what the best RV battery is – both in terms of performance and cost-effectiveness.
What’s Important In The Best RV Battery?
RVs are used in all types of temperatures and weather conditions. RV batteries are a critical part of the power system, with many appliances requiring a charged battery to function property.
The best RV battery will first of all be getting the energy out of it that it says we will. It will also be able to function at different temperatures, as RVers are never in a vacuum. Finally, it will be cost-effective over its lifetime.
The Battery Testing Setup
I told them that the experiments would need to be run with my own parameters for me to do the testing. They agreed not only to this but also to let me rebuild the testing set up with their engineers. So, we got to work.
We built two identical test setups that would feed data into a single data-logging computer.
Equipment Components & Data Logging
The setup was built with a Victron Energy Multiplus Compact 12V 2000kVA 80A inverter/charger used for charging the batteries. 2/0 Cable connected the batteries and the inverters as well as connecting to a set of resistors that can be configured for either an 8 or 80 amp discharge.
A voltage relay controlled the main disconnect relay that we could set or low voltage cut out. An external 24-volt power supply supplied power to the relay was supplied so as not to impact the battery’s discharge.
During each test, both current and voltage were continuously recorded using a National Instruments NI USB-6210 data acquisition system (DAQ) at 1Hz intervals. Voltage dividers with low variant resistors were used to ensure that the voltages conformed with the limits of the DAQ. An AcuAMP DCT 200-10B-24S DC current transducer was used to convert the charge and discharge currents to voltages that could be monitored by the DAQ.
We used two identical freezers with temperature sensors to control the temperatures of the batteries for all tests.
Batteries For Testing
As the purpose of this test was mainly to evaluate different lead-acid batteries vs. lithium-ion to determine the best RV battery, we acquired 4 different types of lead-acid batteries. These ranged from high-end AGM batteries commonly used for high-performance vehicles and RVs, down to cost-effective AGM and flooded lead-acid batteries that can be procured at most national battery retailers.
While Battle Born Batteries’ original cold temperature study only used 2 lead-acid batteries versus 2 lithium-ion batteries, we decided to test a bank of 4 lead-acid batteries against 2 lithium-ion batteries. We thought this would be a more fair representation of lead-acid vs. lithium-ion batteries. By testing four lead-acid batteries, the current would be half of that of the lithium batteries giving them a better chance with the Peukert effect.
As we are not trying to bash any particular battery, we will not disclose the exact brand of batteries used. However, the following data showcases the cost, rated capacity at 20-hour discharge (for the lead-acid), recommended cutoff voltages from the manufacturers, and expected life cycles from the manufacturers.
By getting to define the testing parameters, I was able to make sure we collected enough data to get what I deemed most important. What I am most interested in is the actual energy the batteries can provide.
Amp-hour data is a rating of power and not necessarily directly related to energy as voltage can fluctuate. My goal with these tests was to figure out how much energy each battery delivered under different circumstances.
Comparing energy in Watt Hours will give us an “apples to apples” comparison of each battery test. This allows us to take a look at actual $/Energy or $/Watt calculations to determine which RV battery type is the most cost-effective to own.
Running The Tests
Each test began with fully charging the batteries to their recommended full charge per the manufacturer’s instructions. All lead-acid batteries were allowed to get through their absorption cycle and into float which was usually an overnight charge.
Data logging was begun before tests began and ran after testing to record the voltage bounce back of the batteries. At a 1Hz cycle, we are accurately able to calculate the Amp Hour and Watt-hour capacities that the batteries provided.
Room Temperature Testing
Tests were first performed at room temperature – 70 degrees Fahrenheit. The lithium-ion batteries were discharged to their 100% cut off voltage of 11.8. The lead-acid batteries were first discharged at the recommended 50% cutoff voltage, which is 12.2 volts for the AGMs.
The second set of tests was conducted dropping them to their 80% recommended cutoff voltage at 11.8.
All of these tests were conducted at first an 8 Amp slow discharge. The tests were then run again at an 80 amp fast discharge.
Cold Temperature Testing
Once the room temperature test was completed, the freezers were turned on and dropped to 10 degrees Fahrenheit. All the batteries were tested once again at both the 8 Amp and 80 amp discharge at 10 degrees Fahrenheit.
For sake of time, these tests were all run at 11.8 volts cut off. But by integrating the data, we are able to extrapolate a 12.2 volt cut off amp-hour and watt-hour measurement.
One additional battery was added to the cold temperature test: the newly released Battle Born Heat Battery. This battery has internal heating elements that warm it to the appropriate operating temperature for discharge and charging.
Batteries were charged at 10 degrees F using the same charge profiles as was tested at room temperature. The BB10012 could not be charged at 10F and was brought up to 25F for charging. The BB10012H heated battery was charged in the cold and allowed to remain on and heating itself for 8 hours prior to a discharge.
A second cold-weather test was performed on AGM1 and AGM2 sets at 25 degrees F. We modified the charge parameters to account for the cold temperatures per the manufacturer’s instructions. This is rarely done by a consumer, but we wanted to compare test data against Battle Born’s original 25F data with temperature compensation for charging.
Real World Cold Temperature Testing
Battle Born’s original paper made it look as if most AGM batteries would not work in the cold if set to 12.2 cutoffs. We wanted to see how true this would be, so we charged up the AGM2 set of batteries and plugged in a microwave and coffee maker to the inverter.
We ran these appliances off the cold batteries and watched the load and voltage of the batteries.
9V Drain Test
When we were nearing the end of our time, there was one additional test we wanted to run, which was discharging the batteries all the way down to 9V. This test took a long time to run and we only had time for one set, so we chose the most cost-effective lead-acid batteries, the AGM3, and Flooded set.
This test was run to see how much capacity the batteries could make. The true 50% and 80% of discharge points were extrapolated from the data. The voltage recovered was recorded, too.
We will get into the analysis of each test below, but here are some of the main takeaways from the data.
#1. None of the lead-acid batteries made their rated capacities at the stated cut off voltages from the manufacturer. Even at room temperature with extremely low discharge rates below their 20-hour rate.
#2. The lithium-ion batteries’ performance exceeded their rated capacity at all discharge rates.
#3. The cost per watt-hour delivered for lead-acids was surprising. It was much worse for the expensive AGM batteries than the cheaper options. The flooded lead-acid was the cheapest under all circumstances.
#4. The lifetime cost of all the lead-acid batteries is 2 to 6 times higher than the lithium batteries. Over the life of your RV, this battery is the best.
#5. Lead-acid batteries deliver less power than lithium for the same Amp-hour because of the deeper voltage sag.
#6. The lead-acid batteries have such a high voltage sag in the cold. It’s hard to get power out of them at high loads without lowering the voltage cut-out. Cold weather voltage compensations need to be made to the charging profiles for lead-acid batteries to get acceptable performance in the cold. For the average RVer, this is a bit ridiculous to expect them to do.
#7. Heated lithium-batteries work great! They will self consume some of their energy, so we recommend insulating them for the best results.
Data Files For Your Own RV Battery Analysis
Now let’s take a look at how we arrived at these results with each test. At the end, I will be sharing my recommendations on the best RV battery.
If you wish to review the data or run your own analysis, here is a link to most of the raw test data. This is a VERY big file with millions of data points and your computer may hate you for working in it. It has crashed multiple computers so you have been warned 😉
Room Temperature Capacities
Personally, I think these are the most interesting of the tests we ran. I expected to learn the most from the cold tests, but this data surprised me the most.
Lithium-Ion Battery Capacity
The lithium-ion batteries were tested only once taking them down to their recommended 100% cutoff at 11.8V. These batteries outperformed their rated capacity at the 8A and 80A discharge rates, coming in at 108% and 102% respectively. It feels good to get more than what you pay for. 🙂
Lead-Acid Battery 50% Cutoff Capacities
For the lead-acid batteries, let’s first take a look at the battery capacities we calculated at the different cut off voltages. All of the AGM batteries had a recommended 50% cutoff voltage at 12.2V and the Flooded had a 50% cut of 12.0V.
- Using the 50% cutout, none of the lead-acid batteries were able to make their 50% rating.
- Interestingly, the most expensive AGM (AGM1) performed the worst only making 32% of their rated capacity at the low draw test and 16% at an 80A draw.
- The cheaper AGM 2 batteries could not run the 80A load for long at all before the voltage sagged and the system shut down.
- Using the 12.0V 50% cut for the cheap flooded Lead-acid batteries they almost made their rating at 47% performing the best at the rated 50% test.
One interesting thing to note is that the lead-acid batteries at a 50% cutout made less power than the 2 Lithiums that are rated for full discharge. This will come into play later when we look at the actual cost of energy production.
Lead-Acid 80% Cutoff Capacities
Next, we ran a test down to 11.8V which is the 80% cut out for the AGM batteries. Here is what we found:
- Once again, none of the batteries made their ratings.
- The expensive AGM batteries performed the worst in the low discharge test.
- At this discharge, the 4 AGM batteries did make more power than the 2 lithium batteries, however, discharging them this low will significantly impact their life cycles as evident in the batteries data table above.
I did a quick calculation integrating the data from the 11.8V discharge of the AGM3 batteries to the point when they hit 216 AH capacity – the same capacity as the lithium batteries’ full discharge. Then, I integrated out the calculated watt hours to the same AH discharge of the Lithium.
It was interesting to see that the lithium batteries delivered more energy at 2808 watt-hours at 216AH compared to 2683 Watt-hours of the AGM batteries at 216AH. This is not a huge difference, but I think because the lithium battery maintains its voltage at a higher state for longer it delivered more power.
As stated before, amp hours are not energy and different batteries will provide different energies at the same Amp hour rating. I say it all the time, but I would like to see energy storage batteries rated in Watt-hours, not amp-hours. This is once again another win for the lithium-ion batteries, but we can take this a step further and negate amp-hours altogether and calculate the actual cost per Kwh of each battery.
According to the lead-acid battery manufacturers, there is only one way to get an accurate state of charge estimate. This is from a steady-state voltage after completely disconnecting the load and allowing the batteries to sit for a few hours.
Because this is absolutely not a real-world thing anyone does, we did not do this either. But, we did record for about half an hour after the tests to get an idea of the voltage recovery.
For the low current tests, voltage recovery was not much more than .1 volts so our tests should be very accurate. For the 80A discharge voltage recovery was frequently .4 to .5 volts. Because of this, an 11.8V discharge was probably close to a 12.2V true discharge once the load was removed.
This is an inherent problem with batteries with deep voltage sag. We can either lower the voltage to allow the inverter to work longer and risk damaging the batteries, or leave it at a higher cutoff voltage and miss out on power for larger loads. To address this, you must well oversize lead-acid battery banks to distribute the current across more batteries and keep the voltage drop down.
Actual Battery Cost Per Energy Delivered (Room Temperature)
This is where things start to get interesting. These first calculations were strictly the cost as tested divided by the delivered energy (not over the life of the battery).
This calculation should be independent to battery bank sizes except in heavy load situations where the load will be distributed among more batteries.
From this data, we can see that if you are using a 12.2V cutout to meet the manufacturer’s 50% recommendation, the lithium batteries are actually cheaper than both the expensive AGM and only slightly more than the cheap AGM!
The cheap, flooded lead-acid batteries are clearly the winner on the cost-effective per energy delivered calculation a low 8A discharge. When taking a look at a discharge to 11.8, things get a bit better for the AGM batteries and the cheapest AGM performs at almost half the cost of the full discharge lithium.
High Load Discharge Cost
This is where lithium-ion battery technology really shines.
Because they exhibit so much less of the Peukert effect, they always deliver more energy at high discharge rates than a lead-acid alternative. This becomes clearly evident in the cost of running high discharges as well. Take a look at the rightmost column of the Cost Per Energy Delivered Table above.
Both expensive AGM performed so badly that the lithium is much more cost-effective.
Note: The $91 number for AGM2 came from the fact that the voltage sagged so badly under load that at 12.2 it cut out almost immediately. Surprisingly, the cheap AGM3 batteries performed okay along with the flooded 6V set in series.
Lifecycle Costs (Room Temperature)
After looking at the $/Wh cost results in the table above, it appears that the flooded lead-acid batteries are the most cost-effective battery to own, followed up by the cheapest AGM.
However, this does not account for the lifecycle of the battery and is only an instantaneous measurement.
Lifecycle is defined as how many times the battery can discharge before reaching its end of life (EOL). EOL from a battery manufacturer’s perspective is when the battery can only hold 80% of its original rated capacity. Manufacturers provide estimated cycles before this happens.
Here is the chart for these estimated cycles for each battery on the right-hand side for 50%, 80%, and 100% depth of discharge (DOD).
The lifecycles are heavily dependent on how deeply the battery is discharged. So, we can now take our data and calculate a lifecycle cost per battery with the following equation.
Lifecycle Cost per Watt Hour = Cost of batteries / (delivered Watt hour X Lifecycle numbers)
We ran this calculation (divided by 1k to get in Kilowatt hours instead of watt hours) and got the following results. This is where we find out which RV batteries we should be spending our money on!
Because of voltage recovery effects of lead-acid batteries, these numbers calculated at an 8 A discharge (2A per battery) should be an accurate representation of cost at a best-case scenario for lead-acid.
The Most Cost-Effective RV Battery
It is clear that lithium batteries are the cheapest to own over their life.
It is also interesting to see that the expensive AGM still remains expensive and provides no energy benefit at all. Seeing lithium as the cheapest option is exactly what I expected. But, I did not think it would be by this big of a margin being 2-6x less expensive.
As mentioned before, this is really the best-case scenario for lead-acid. It’s unlikely that the energies we got in the tests could be attained in real-world scenarios. Lead-acid is very sensitive to loads and charging. When not used per their specifications they perform even worse, so this is the best case data.
Real-World Lifecycle Tests Suggest Even Poorer Lead-Acid Performance
In addition, I procured some real-world test data from early tests performed by Battle Born Batteries against the same AMG 2 Battery Brand. These tests were performed at a 50A discharge (25A equivalent per battery), which is much higher than we ran but down to 11.8 or an 80% cutout.
It’s interesting to note that their data reflected an initial capacity around 140Ah, or about 60% similar to the numbers in our experiment. The battery in their experiment hit its 80% capacity at only 100 cycles with an 80% discharge. Note that they were not allowing for voltage recovery on a high discharge so it was not a true 80% discharge, and the life was still terrible.
If this is real-world performance (and likely usage by an RVer) then the lifecycle cost numbers will be much much higher than calculated.
Cold Temperature Battery Testing
In addition to running room temperature tests, I ran some cold temperature tests. The batteries were placed in freezers with plenty of airflows to make sure they got really cold.
This was also an opportunity to test out the Battle Born BB10012H Heated Battery. This battery has internally heated strips that keep the battery at optimal operating temperature for both charging and discharging.
10 Degree F Cold Temperature Testing
I had a limited amount of time to run the tests. So, we only ran 11.8V cut voltages and repeated the same tests that we ran at room temperature. This time we ran them at 10 degrees F, including the same charge parameters.
All of the batteries showed degraded performance in the cold. We see about a 20-25% loss across the board compared to their room temperature performance at a low discharge rate. When comparing at a higher discharge rate this percentage was much worse for the lead-acid batteries.
This is due to the Peukert Effect being exaggerated for lead-acid batteries in cold conditions. This was a key takeaway from Battle Born’s original cold temperature whitepaper.
Matt from Adventurous Way did a great write-up about their paper and this effect. He graphed out the capacity loss at load in cold weather, shown below. Matt has a degree in physics and is a really smart guy with whom I discussed these results in detail.
Read his analysis here: Battle Born Cold Charging Study: Analysis
Battle Born Heat Battery Performance
Taking a look at the Battle Born heated battery performance reveals some interesting data as well. The heated battery should have a very similar capacity to the standard 100Ah setup but actually gave us less discharge capacity at the low discharge rate. This was due to the batteries heating themselves and using some of their energy to keep warm.
The heat was turned on 8 hours prior to the test. The batteries were all completely uninsulated and spaced apart for best cold airflow. So, this was the worst-case scenario for the heated battery.
Regardless, it stayed warm and was able to be recharged as normal even in these cold conditions.
It performed better in the 80A test than the non-heated version because the runtime was so much shorter, it was less time that it was heating itself. The standard lithium battery could not be recharged in the cold to run the 80A test and had to be warmed up to 25 degrees to charge, then cooled off again.
For cold-temperature RVing, this is your the ultimate best RV battery choice.
25 Degree F Battery Testing With Charging Compensation
I wanted to give lead-acid the benefit of the doubt, so we warmed the batteries up to 25 degrees. This is a more likely RVing temperature. We also changed our charging parameters to compensate for the cold. This includes charging at a higher voltage per the manufacturer’s specification.
It is rare that users program temperature voltage charging compensation into their lead-acid systems, so this is an unlikely scenario. But we did it anyway. Interestingly, the batteries performed no better than the 10F discharge at the 8A slow discharge. But, they almost met their original room temp performance at the high discharge current.
Real-World Cold Temp Example
Before we were done with the cold temp tests, we wanted to see what would happen in a real-world cold temperature scenario. We charged the batteries one more time at 25F and set up some tests with a microwave and coffee maker – two tasks an RV battery might be asked to perform.
Using the inverters, we plugged in and put a load on the AGM3 batteries and logged their performance. We started with an 11.8V cutout and was only able to run the coffee maker for about 2 minutes before the inverter cutout. Then we dropped the voltage to 10.6 and continued the test and completed our coffee.
We then plugged in a microwave and ran for another 7 minutes, at which point it worked. When turning off the microwave the voltage bounced back to above 12.3 volts.
This showcased a real-world problem with the lead-acid batteries in the cold. The significant voltage drop needs to be compensated for to use the batteries. It’s safe to lower the voltage for short periods of time, but must be monitored occasionally at a steady-state so as not to drain them too far. Because of the cold temp Peukert change, even a shunt-based battery monitor will not accurately read the state of charge for cold lead-acid batteries.
9V Drop Test
In our final test, we allowed our most cost-effective lead-acid batteries to discharge way beyond the recommended stop points. We wanted to see if they could make their capacity. We used our 8A slow discharge and ran them down to 9V at room temp of 70F.
Note: This is never recommended for a lead-acid battery as it will damage it even with one discharge like this. Since these were test batteries, we went for it.
AGM3 9V Drop Performance
The AGM 3 batteries almost made their entire rated capacity coming in at 97.48 percent. After integrating the load data, I determined that the true 50% voltage was at 12.0V (should be 12.2 according to the manufacturer).
Unfortunately, these batteries only recovered to 10.9V which is well below the recommended steady-state voltage, so irreparable damage was done.
Flooded Lead-Acid 9V Drop Performance
The flooded lead-acid batteries cut out sooner, only providing 86% of their capacity and the 50% was calculated at 11.9V (12.0 according to manufacturer). These batteries recovered to 11.6 which is interesting that even at such a low load they didn’t fully discharge.
We could have run these tests lower than 9V but there really isn’t any point as 9 V is well below what any electronics should run at anyway.
Best RV Battery Testing – Conclusion and Recommendations
Truthfully, the data we acquired shocked me as I was gathering it. Nichols’ statements about not being able to achieve capacity seem true as all the lead-acid setups had trouble making their ratings. It would be hard to get them to perform any better in real-world situations.
Lead-acid batteries are too sensitive to environmental, load, and charging conditions to be used reliably in a power storage system. Compared to lithium-ion batteries, I can no longer recommend them.
I used to recommend them as a cheaper alternative, but after seeing the cost data even that does not make sense. The lifetime cost is so much more expensive than lithium – and that doesn’t even factor in replacement costs and labor.
When To Use Lead-Acid?
Lead-acid batteries do one thing very well, they provide great amounts of current for very short periods of time. As long as they are immediately recharged, they can have a good life. This makes them good for engine starting batteries and I don’t think they will be replaced any time soon (but it will eventually happen).
As for power storage, they are all terrible. Paying for expensive AGM or flooded batteries does not seem to get you any better performance and is a waste of money. If you truly cannot afford lithium, get the cheapest lead-acid batteries you can and save your money for lithium next time.
Consider, however, that you can get away with half the lithium capacity vs lead-acid and get even better performance, as seen in this study.
Cold Weather Use?
In cold weather, lithium still outperforms lead-acid and can be used, they just must be warmed prior to charging just like lead-acids. Heated batteries are a great way to get around this. We recommend insulating them so as not to waste energy keeping them warm. Lithium-ion batteries don’t need to be vented, so they can easily be installed in an enclosed space that’s easy to warm and not worry about them.
The Best RV Battery For The Money
Lithium-ion battery benefits have been understood for a long time, but they’ve always had the downside of “being more expensive.” Well friends, per our test results, this has been disproven. The best RV battery out there is also the most cost-effective over its life.
And that isn’t even factoring in the quality of life benefits of never having to buy/replace another battery or worry about state of charge again!
Technology marches ever forward and with it, batteries. It’s amazing that lead-acid has hung on as long as it has, but it’s truly an outdated technology for energy storage. These tests were the final nail in the lead-acid coffin for me. I will no longer be looking at or even considering lead-acid for anything other than starting batteries.
As they say at Battle Born, “Lead is Dead.”
If your interested in learning more about Battle Borns Products check them out here: Battle Born Batteries
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