LiFePO4 storage

[dryfly]

From what I have read on various manufacturer's websites, it is recommended to store lithium batteries at 40-50% SOC. Apparently due to the battery chemistry, storing at full SOC will shorten the life of the battery.

How does this apply to those who full time in their RV, being on shore power and keeping the battery at full charge by using the float mode of their converter/charger? I'm sure full time use does involve some cycling of the battery, but with shore power in play I would imagine very little.

Also, for those that occasionally use their trailer, do you take the time to discharge the battery to the reduced state of charge before storing it?

 

[Second Chance]

We have 4 100AH Battle Born batteries installed in the Solitude (with a PD lithium-specific converter-charger) and the rig is on shore power almost all the time. No issues whatsoever.

Rob

 

[triplethreat]

From what I have read on various manufacturer's websites, it is recommended to store lithium batteries at 40-50% SOC. Apparently due to the battery chemistry, storing at full SOC will shorten the life of the battery.

How does this apply to those who full time in their RV, being on shore power and keeping the battery at full charge by using the float mode of their converter/charger? I'm sure full time use does involve some cycling of the battery, but with shore power in play I would imagine very little.

Also, for those that occasionally use their trailer, do you take the time to discharge the battery to the reduced state of charge before storing it?

Being full time means that you are not really "storing" your battery, in the sense that they are referring to about LFP storage. If I were in that situation of being full time, what I would probably do is maybe once every couple of months or so, turn off the Converter/Charger at the 120VAC breaker that feeds it. If you have solar charging, you would want to disable that too. Then run the 12VDC stuff off of the battery only, with all the charging sources disabled, as explained above. Monitor the battery SOC and take it down to maybe 20% SOC, then re-enable the charging sources.....Converter/Charger and the Solar charging.

Another possibility is this....if you can adjust or change the "float" voltage of the charging sources, move the float voltage down to something like 13.4V (3.45 volts per cell and 4 cells inside the battery). A LiFePO battery will eventually become fully charged at around 13.8V.....but it takes forever and that is why the bulk charge voltage on many of the LFP chargers are at 14.4 or 14.6 volts. Setting the float voltage to 13.4 will not harm the battery, and the plus side is that it is a low enough number to NOT bring the battery to full SOC. Hope this helps.

 

[Jomani]

Personally, I think the effects of storing at 100% SOC are still somewhat unknown. The newest evolutions of LiFePo4 and BMS technology have yet to fully come of age as far as longevity - remember, these things should last ten years so it will take time for everyone to fully understand the long term effects.

Having said that, I do try and hedge my bet when it comes to storage. When I return from a trip, I generally leave my rig sitting on the street in front of my house while I unpack, clean out the fridge, etc. During that time, I shut down my solar and run lights and fridge off batteries. By the time I get her backed into her resting space, the batteries are generally at about 80% - where I leave them until I get ready for the next trip.

If I were full timing with LiFePo4, I think I would try and exercise the batteries no less than once per month. Like @triplethreat mentioned, just flip off the converter and solar and let the batteries draw down to about 20%. I think that is important to help keep the battery’s internal cells balanced.

 

[triplethreat]

Also, for those that occasionally use their trailer, do you take the time to discharge the battery to the reduced state of charge before storing it?

Sorry, I forgot to respond to this part of the question, so here goes. My winter storage for the batteries involve leaving them in the trailer, as we very seldom get below zero temperatures here in E. TN. So after I'm done with the standard winterization of the trailer, I discharge my battery (302AH DIY that I built in 2022 from 4 of the EVE LFP cells). I bought a 200W, 12VDC heater strip and it's just a heat strip with no fan of any kind. So I hook it up to the battery and let it hang in the front compartment with a small 6" or 8" fan blowing on it to dissipate the heat that it's producing and not burn it up. That heater will pull somewhere around 17/18 amps out of the battery, and I do a quick calculation to "guesstimate" how long it will take to bring the battery down to around 50% SOC. When I reach that point, as determined by the DALY BMS or my Victron 712, I shut off the main battery switch (300A switch I installed) and remove the heater. That is how the battery sits all winter long.....very slowly self discharging a bit, and the BMS using milliamps of current too. From sometime in early November or late October, until early April, it will go from the 50% SOC down to the upper 30s SOC. I usually check on it about once a month, just to make sure nothing unexpected has happened. And with the 300A Battery disconnect turned off, there is ZERO chance that the converter/charger can possibly try to charge the battery in the below freezing conditions if we have them. Plus, the DALY BMS also has a low temperature cutoff for charging, so I have that set to prevent it also. Hope this helps.

Here is a pic of the type of heater strip I'm talking about. I just looked it up on Amazon, where I purchased it, and it's no longer available there....but there are others out there I'm sure.

 

[dryfly]

Thanks for the interesting replys. I agree this technology is new enough that the long term effects of 100% SOC are still unknown.

The reason I ask this question is that I mentioned in a previous thread that I need a 100AH battery for backup purposes around the house, and I would like it to be available in a 100% SOC if needed. Without exercising the battery monthly, this doesn't look doable. I may just have to be happy with the 50 AH capacity that would be available on an emergency basis, then recharge.

 

[reubenray]

What if I have solar power in my storage yard to keep my LifePO4 battery charged?

 

[triplethreat]

Thanks for the interesting replys. I agree this technology is new enough that the long term effects of 100% SOC are still unknown.

The reason I ask this question is that I mentioned in a previous thread that I need a 100AH battery for backup purposes around the house, and I would like it to be available in a 100% SOC if needed. Without exercising the battery monthly, this doesn't look doable. I may just have to be happy with the 50 AH capacity that would be available on an emergency basis, then recharge.

The LFP technology has been around long enough that the patents for it began to expire in 2022.....so it's safe to say well over 20 years. When that happened, the onslaught of new battery manufacturing began and has served to drive prices way down for them. I think it's a pretty clear that LFP batteries do better when NOT stored longer than 6 months at full SOC. It's also one of the reasons that I personally will not use a charger for mine that puts 14.6V to the battery in bulk mode. My charger is set/configured to 14.2V in bulk or constant current mode, and then switches to constant voltage and then finally, float voltage, which as I stated earlier I have set up for 13.4 Charging at the 14.6v level is the max the battery should ever be exposed to, and to me, there is no sustainable/good reason to charge at that level and subject the cells/battery to their extreme voltage limits....14.6V for the entire battery or 3.65V per cell in the battery. BattleBorn is one of the few manufacturers that suggest 100% SOC for storage.......I totally disagree with that statement.

 

[triplethreat]

What if I have solar power in my storage yard to keep my LifePO4 battery charged?

You really don't need to keep it fully charged, if it is in Winter Storage for several months. Just make sure you have a way to totally disconnect the battery from the trailer (either a full cutoff switch that kills all the power to and from the battery, or remove the Pos. lead from the battery terminal. LFP batteries self discharge at a much lower rate than Flooded Lead Acid (FLA) batteries do. Put the trailer into storage at say a 60% SOC and it will self discharge at approx. 2% per month.

The Large Red switch that you can see in this picture is my Total Battery Disconnect Switch (300A rating) Turning that off prevents any drain on the battery or any chance of charging it when temps are 32° or lower and damaging the battery. I have other safeties in place also, but that is what many of us use....or similar...

The 1/0 Red lead on the right side of that switch goes directly to the inline fuse that is mounted on the battery POS. terminal.

 

[BoredWeasel]

I will intentionally deplete my batterys a bit before storage. I turn off batterys charging ability on th e BMS, I use solar overkill, and run the dehumidifiers and ac while we get it cleaned up at the storage facilitys.......While it isn't down to 50% it certainly is down to 80 percent or lower.

My thought is the folks that know more than me are doing it and it doesn't harm the batterys.

I have stored mine in sub zero temps in the trailer over a couple of winters with no apparent isssues. The HUGE caveat to that is make sure they are above freezing before you allow them to charge.

 

[triplethreat]

I will intentionally deplete my batterys a bit before storage. I turn off batterys charging ability on th e BMS, I use solar overkill, and run the dehumidifiers and ac while we get it cleaned up at the storage facilitys.......While it isn't down to 50% it certainly is down to 80 percent or lower.

My thought is the folks that know more than me are doing it and it doesn't harm the batterys.

I have stored mine in sub zero temps in the trailer over a couple of winters with no apparent isssues. The HUGE caveat to that is make sure they are above freezing before you allow them to charge.

I would agree, 80% is better than 100% SOC for storage. 80% SOC is approx 13.25V for the battery or 3.31 per cell. And while that doesn't sound like much difference between the full SOC voltages and the 80% voltages, it's enough to keep the battery/cells away from at least some stress that they would have at full voltages and full SOC.

We sometimes get some very cold (for our area) and for a "just in case" scenario, when I built my battery box for the DIY battery I built, the box is insulated AND heated. If you look at my picture in post #9, the larger gray square box has a digital temperature controller inside it. It can be turned on/off as needed and has it's own temperature sensor which is buried in between #2 and #3 cells in the battery cell array. I've got it set (if I turn it on) to turn on four 7watt heat strips inside the battery box which provides ~28watts of heat inside which can slowly bring the cell's temperature up and out of the danger zone of 32°. That temperature can be monitored on the controller or I can look at my BMS app and see what temperatures the battery/cells are seeing. It's probably "overkill" for my situation, but hey, it's something that I sometimes do.

 

[Jomani]

@triplethreat it sounds like you have certainly done your share of research on LiFePo4 technology. The technology was first developed in 1996, so yes, over 20 years ago. Where it gets interesting (for me at least) is that they have just recently started to figure out exactly what is causing degradation. I came across an interesting article a while back (I will link to it below) that dives deep into LiFePo4 storage and degradation.

While I don’t claim to understand everything this article talks about, I would offer this quote that seems to indicate that, while state of charge is indeed a factor of degradation, depth of discharge seems to be a bigger factor.

“For illustrative purposes, Fig. 5, Fig. 6 depict the capacity fade characteristics (6), (7) obtained in [26] from the accelerated aging tests. Particularly, Fig. 5 illustrates that capacity fade from idling (6) is slower when the battery SoC is kept low. From this figure, one can infer that it is in general better to keep the battery discharged when the service is not required. On the other hand, Fig. 6 suggests that capacity loss from cycling (7) is the most severe for high DoD and low median SoC. Thus, to decrease capacity loss from cycling, one would want to charge and discharge the battery around the highest possible SoC. Obviously, the above degradation mechanisms disagree and require a balanced trade-off to ensure optimal battery utilization.”

https://www.sciencedirect.com/science/article/pii/S0306261922004688

 

[BoredWeasel]

I am not to worried about my batterys lasting 10 years, with the way the price is crashing I could replace what I currently have for half what I paid for them 4 years ago. I think most won't own the same Rv in 10 years anyhow.

The SOC discussion reminds me of the to compress or not compress the individual cells when building your own pack......or polishing the terminals or the Brand of bms

 

[triplethreat]

LOL.,. I compressed, polished, and then went with DALY. Hey, 2 out of 3 ain't too bad!

 

[BoredWeasel]

I had two daly on my packs and one of them stopped working right and wouldn't fully charge one of my two batterys.......I didn't compress or polish.....LOL again figured i would sell the packs with the trailer.....well I didnt and they moved too the GD, they are so much better than a BB

 

[Butcher]

Many of the batteries you can access the BMS with Bluetooth and you can set it to not charge above a certain voltage. That voltage can be set to the point it would not charge above 50%. You could also play with the settings so that the batteries will drain to a voltage of about 50%. That way, those that store their RV away from your property, can leave the RV on and at some point, the battery will drop to 50% and keep it that way till next season.

I hope that makes sense.

 

[TimtheToolMan]

There sure is a lot of good information on what affects LFP, but still not enough to know how long the batteries will last under real world conditions. As previously stated in different terms, the prices are no longer so high that a mistake in use/care is not extremely painful to the pocketbook for most owners.

I plan to remove batteries, during storage or when temperatures are extremely high or low. At 22 pounds for each of the two small profile group 24 batteries (mounted in camper) and Anderson quick release connectors this is easy, fast and reasonable. This was not remotely practical with the two GC2 at 66 pounds each, while they did not like the temperature extremes either, which were still mounted on the TT tongue.

I will turn off TT power switch when using shore power and have a note at supply outlet to turn off switch when connecting cord.

I will take the extra steps in hopes of extending battery life but mostly for hopes of reliability. At $600 for two batteries, if life goes from 7 years to 10 years that is a savings of only 30% $200. $200/10 years is $20/year so I would only be saving a small amount per year! Much effort for this saving is questionable at best.

More information on best practices--video good also. Cycling at 0-20% provides best life or stating it differently, average SOC over life of battery matters. It also gets into discussion of 100% SOC and when this makes sense.

New Study Raises Questions About LFP Battery Charging Habits

 

[reubenray]

I am planning on moving my single 100ah lithium battery from my tongue to the front compartment this off season. The tongue location is a PITA to remove the battery. I will need to check into the Anderson quick release connections. I also will have to drill into the frame and then the compartment floor to get the cables to the battery. I may have to change out the battery cables also. This is why I will do this during the off season. If I decide to remove the battery during the cold it will be easier.

 

[triplethreat]

I am not to worried about my batterys lasting 10 years, with the way the price is crashing I could replace what I currently have for half what I paid for them 4 years ago. I think most won't own the same Rv in 10 years anyhow.

The SOC discussion reminds me of the to compress or not compress the individual cells when building your own pack......or polishing the terminals or the Brand of bms

The cell data sheet that came with my EVE 304AH cells, show a "cycle life" of equal to or greater than 3500 cycles at 25°C (77°F). So if you look at that from a real world perspective and 365 days a year.....that would work out to 9.58 years. How many folks charge and discharge (One cycle) every single day of the year? Even if you are full timers and actually do discharge/charge every day.....the battery is not really being stressed if you are plugged into shore power (converter keeps the battery topped off). For well over the majority of us, who do not full time and use the camper on an occasional basis......even half of the year, that would theoretically double that 9.58 number to 19 years. If the data is accurate AND there is no premature failure, it's very likely that the battery(s) will outlast the trailer.

 

[dryfly]

Thanks for all the info to my OP. Looks like paying close attention to SOC will definitely increase lifespan of the battery. This is another example of the complexity of things today. In the old days we went to Walmart, bought the cheapest battery we could find, stuck it in the trailer, and bought another battery in 3 years. No thinking needed. This seems true with everything we buy today. Nothing is simple anymore, but the technology is mind blowing! I just read an article on Solid State Lithium batteries. The quest for knowledge never ends..................