Care and feeding of LiFePo4

[Lysergeon]

Hi all, I know this is an old thread but, just looking around the internets on who knows what about lithium, and you all seem to really know what you are talking about!

I am wondering your thoughts on my situation, I have 2x100ah PowerRoad Lithium Batteries(with built in bluetooth monitoring (BMI), and a progressive Dynamics PD9180ALV converter.

This has all been working great off grid, but now I am on an RV pad for the winter with shore power. (will be living in the unit, its actually a class A, sorry for sneaking into your forum! But you guys seem to really know your stuff!)

I would rather not disconnect the batteries completely as I may need to move the RV at various times throughout the winter and will need them (and I am not very confident with these processes and live in an area where it is hard to find help to do so, so having to remove and then re-install the batteries from converter/inverter etc would be a huge pain)

So, I am currently on shore power, and my batteries automatically stop charging with their BMI at 100% SOC (which shows at about 13.5/13.6v on the monitor) on either battery. However I hear this is bad for the batteries to stay at this SOC... would I be crazy to not just disconnect the batteries all together?

How "bad" and or damaging is it leaving them at 100%? It looks like the cells themselves are sitting at a nominal voltage individually (about 3.4v or less each) and that seems to be about 70-80% and they are disconnected from the system with their own automatic protection from the batteries BMI... so... is it a big deal if I leave them connected? Does anyone know have any real data on this?

If I left them like this for say 4 months, it doesn't get super cold here, -5 celsius at worst and that is very rare.. so..

Also, I can fairly easily throw the breaker to shore power and drain them down and recharge them.. would that be helpful to do every say week or 2?

Hoping to find some "best" solution that doesnt involve disconnecting everything..

Thanks so much in advance!!

[@Michael]

Progressive Dynamics charge profile for their 9100 series Lithium models is vague. They imply that it's not OK to store them with the charger attached. But they have an add-on "Charge Wizard" that seems to alter the charge profile, but not for Lithium batteries.

(which shows at about 13.5/13.6v on the monitor)

That's not to bad of a voltage for storage of LiFePo4's, if it stays around that level. If the charger was holding the voltage higher than 13.6 it might be an issue.

Also, I can fairly easily throw the breaker to shore power and drain them down and recharge them.. would that be helpful to do every say week or 2?

I would not do that.

[markopolo]

My 2 cents: (currently)

Storage voltage: 13.1V to 13.2V if left on charger for months.
Standby voltage: 13.4V if left on charger for months.

Storage is when unused and no use is anticipated.
Standby is when immediate use is a possibility such as expected power outage due to an approaching storm etc.

13.6V is actually a charging voltage for LFP. It's slow but the battery will get to or very near 100% and be held there. It could be thought of as being a float voltage meaning that the battery is held at a voltage higher than it would naturally rest at.

Degradation of the battery is inevitable. The rate of degradation is what matters. It has been reported that some LFP batteries degrade quickly if left at a high state of charge even if left off charger. See: https://marinehowto.com/lifepo4-batteries-on-boats/

“The cells lost 11.6% of their confirmed capacity just sitting at 100% SOC”

UPDATE: We have now completed a second round of this type of testing with a brand new prismatic cell. The difference was rather dramatic and I have no explanation as to why? The second test we did went for 13 months, under identical testing criteria, and this cell only lost 3.8% of previously verified Ah capacity. While this is quite a bit less capacity loss it still lost capacity.

How can LFP cell manufacturers suggest that the mere act of storage, at 100% SOC, is bad for the cells, which we have physically tested and confirmed is degrading them, and then suggest it is okay to float? How can they say “store at 50-60% SOC” yet then give you a “float” voltage?

Cycle or disconnect:

Is the rate of aging and capacity loss greater if the not needed or hardly needed battery is cycled or disconnected compared to being held at Storage, Standby or Float? My guess is that it would be (ranked from best to worst): #1. Disconnected left at 50% SOC, #2. Storage at 13.1V to 13.2V, #3. Cycled down to 20% SOC then recharge, #4.Standby at 13.4V, #5. Float/charger at 13.6V+.

[avanti]

Originally Posted by markopolo

Is the rate of aging and capacity loss greater if the not needed or hardly needed battery is cycled or disconnected compared to being held at Storage, Standby or Float? My guess is that it would be (ranked from best to worst): #1. Disconnected left at 50% SOC, #2. Storage at 13.1V to 13.2V, #3. Cycled down to 20% SOC then recharge, #4.Standby at 13.4V, #5. Float/charger at 13.6V+.

I am also curious what the self-discharge rate is for Li.

Decent AGMs have almost negligible self-discharge. I recently retrieved a coved-quarantened car after 18 months with the battery completely isolated. Started right up without a hiccup.

[Lysergeon]

Wow thank you all for the quick replies.. well it sounds like I had better just get used to adding and removing the batteries, else waste a heck of a lot of money..

Any specific order I need to remove the cables (pics attached) like I said I am not very confident in these matters so not 100% sure if I will electrocute myself or end up destroying equipment, lol.. of course I will ensure everything is off first.. (store switch... breakers?) Should there be zero voltage on the lines when I disconnect or is that even possible? I have a volt meter..

Thanks again all, much appreciated.

[markopolo]

Before removing, contact Progressive Dynamics https://www.progressivedyn.com/contact/ - and find out exactly what the charger does.

Is it a continuous 14.6V output?
Does it charge to 14.6V & then quit charging?
If so, at what voltage does it resume charging?
If it resumes at a much lower voltage that might be good enough.

Removing the batteries would be the last thing I'd do. Hopefully the charger is on it's own breaker at the panel in the coach - that would let you disconnect the charger while leaving the coach plugged in.

[Lysergeon]

I will ask them Marko, thanks.

[Davydd]

I went for 6 years with my lithium ion batteries plugged int shore power at 100% charged. First two years outside in Minnesota but I had heating pads that kept them above 41 deg. For 4 years I had inside storage where I kept the garage at a minimum of 50 deg. In the garage it was my man cave for bathroom and beer so I kept it plugged into shore power. I could have disconnected by flipping a switch. My batteries were custom packages, not car battery size inside a cover and steel cage under the floor weighing over 400 lbs. I couldn’t remove them if I wanted to.

Lithium batteries have an aversion to cold weather storage. You don’t have to remove them if you have a method of keeping them above 42 deg. connected or disconnected. That’s mostly for charging. Batteries of various makes can be safe if above -4 deg. or -40 deg. as it once said my manufacturer (Valence) batteries could do which is the same as AGMs. You also need to disconnect you chassis AGM battery as they have power leaks. That’s another reason I’ve alway kept my van plugged into shore power as I have a Trick L Start charge for the chassis battery.

It is just more convenient to leave lithium ion batteries plugged into shore power. The major concern is keeping them above freezing and there are many ways externally to accomplish that especially if you periodically want to use you van during winter storage.

[Lysergeon]

Originally Posted by Davydd

I went for 6 years with my lithium ion batteries plugged int shore power at 100% charged. First two years outside in Minnesota but I had heating pads that kept them above 41 deg. For 4 years I had inside storage where I kept the garage at a minimum of 50 deg. In the garage it was my man cave for bathroom and beer so I kept it plugged into shore power. I could have disconnected by flipping a switch. My batteries were custom packages, not car battery size inside a cover and steel cage under the floor weighing over 400 lbs. I couldn’t remove them if I wanted to.

Lithium batteries have an aversion to cold weather storage. You don’t have to remove them if you have a method of keeping them above 42 deg. connected or disconnected. That’s mostly for charging. Batteries of various makes can be safe if above -4 deg. or -40 deg. as it once said my manufacturer (Valence) batteries could do which is the same as AGMs. You also need to disconnect you chassis AGM battery as they have power leaks. That’s another reason I’ve alway kept my van plugged into shore power as I have a Trick L Start charge for the chassis battery.

It is just more convenient to leave lithium ion batteries plugged into shore power. The major concern is keeping them above freezing and there are many ways externally to accomplish that especially if you periodically want to use you van during winter storage.

Hi David, thanks for the input! So, you never noticed any significant loss of ah or voltage after all this time plugged in? If so that is great to hear, as far as the cold, it shouldnt be an issue, as I said coldest it gets here is-5 which these are safe to sit in, especially if the batteries won't be being charged.. and in any case, on the colder nights I could put a small heater in the battery compartment, so should not be an issue at all.

So, seems like at least a couple of you think it should be fine.. but a few others saying I will almost certainly damage them haha... so no clear conclusion here.. of course I am going to be inclined to go with the easier solution if its 50/50, which would be to leave them connected..

I have been on shore power now for about 3 days with the batteries connected.. they are sitting in "standby" mode.The stats are as follows:
Battery1 13.48v steady. cell voltages @ 3.338, 3.339, 3.459, 3.344
Battery2 13.52v steady. cell voltages @ 3.485, 3.354, 3.344, 3.346

From what I have read, these cell voltages are within the "storing" range (nominally 3.4v) so... if the internal BMI has locked them from taking any more charge... it seems to me it should be relatively safe... I will put a ticket in with Progressive Dynamics and see how the converter works, if it will try to force charging them higher at some point or not... but its designed for lithiums so you would think it would "know" better.

Thanks again all, and I still welcome any further input! I have been on a few forums with this and this one has been by far the most helpful within a day!

[markopolo]

I don't think David knows how much capacity was lost over the 6 years. If he does know then I don't think he has shared that info on the forum. It would be very useful to know for sure. Did they lose 1%, 5% 15% ? ? ?

Originally Posted by Lysergeon

...................................

I have been on shore power now for about 3 days with the batteries connected.. they are sitting in "standby" mode.The stats are as follows:
Battery1 13.48v steady. cell voltages @ 3.338, 3.339, 3.459, 3.344
Battery2 13.52v steady. cell voltages @ 3.485, 3.354, 3.344, 3.346

.......................

Parallel batteries would be expected to be at the same voltage. Both at 13.48V or both at 13.52V for example. If they are in parallel then maybe it's a BMS calibration error. What is "standby" mode? Is that something you initiate or does it mean just an idle (not in use) battery?

The voltage difference in the series connected cells seems very large to me. 3.459-3.338=0.121V & 3.485-3.344=0.141V. For comparison, I just looked at my 3 batteries and the greatest difference is 0.004V. One of the batteries shows only 0.001V difference between the 4 cells. Mine have been sitting unused for about a month. I'd suggest contacting the vendor to find out if the BMS does balancing and if so, at what voltage does balancing occur. Certainly keep monitoring it over time to see if it changes when in use etc.

Maybe someone else here will comment on the cell imbalance. I've never seen it that high but I only have experience with my 3 DIY battery packs.

[@Michael]

Originally Posted by Lysergeon

...as I said coldest it gets here is-5 which these are safe to sit in, especially if the batteries won't be being charged.. and in any case, on the colder nights I could put a small heater in the battery compartment, so should not be an issue at all.

Correct - you would not want to remove the batteries just because of the cold if you can keep them from charging when below freezing, and keep them going under -4F when not charging.

Originally Posted by Lysergeon

I have been on shore power now for about 3 days with the batteries connected.. they are sitting in "standby" mode. The stats are as follows:

Battery1 13.48v steady. cell voltages @ 3.338, 3.339, 3.459, 3.344
Battery2 13.52v steady. cell voltages @ 3.485, 3.354, 3.344, 3.346

I tried (and failed) to find information from your battery manufacturer that would indicate what they expect for a proper charge profile. BattleBorn, for example, says that 13.6v float is fine. "Bulk/absorb = 14.2V–14.6V. Float = 13.6V or lower." The mfg. of your batteries might have information that helps.

The option that you can also explore is to see if the Progressive Dynamics converters will function as power supply when not connected to a battery. If so, then you can simply disconnect the lithium batteries and run your 12V directly from converter. It looks to me like there is a button on the top of the battery that shuts it off. If that's what that button if for, then there is no need to un-wire anything.

[Lysergeon]

Originally Posted by markopolo

I don't think David knows how much capacity was lost over the 6 years. If he does know then I don't think he has shared that info on the forum. It would be very useful to know for sure. Did they lose 1%, 5% 15% ? ? ?



Parallel batteries would be expected to be at the same voltage. Both at 13.48V or both at 13.52V for example. If they are in parallel then maybe it's a BMS calibration error. What is "standby" mode? Is that something you initiate or does it mean just an idle (not in use) battery?

The voltage difference in the series connected cells seems very large to me. 3.459-3.338=0.121V & 3.485-3.344=0.141V. For comparison, I just looked at my 3 batteries and the greatest difference is 0.004V. One of the batteries shows only 0.001V difference between the 4 cells. Mine have been sitting unused for about a month. I'd suggest contacting the vendor to find out if the BMS does balancing and if so, at what voltage does balancing occur. Certainly keep monitoring it over time to see if it changes when in use etc.

Maybe someone else here will comment on the cell imbalance. I've never seen it that high but I only have experience with my 3 DIY battery packs.

Hmm that is interesting that your cell voltages are so closely aligned. I will definitely try to get more info from the manufacturer on this. Sadly I don't have any data on if they were like this to start with or became misaligned over time. It could be that the manufacturer just didn't use matched cells to start with. I know battleborn matches them this way, unfortunately I didn't know any better when I got these installed (the rv/solar dealer recommended these).

As far as the standby mode, if there is no draw they go to standby, or if there is any issue (under voltage or over vtage protection etc) they kick into this mode automatically. So in this case, once they charged to 100% off of the converter, they automatically switched to standby to protect themselves.

[Lysergeon]

Here is some data from today and yesterday... not sure if it helps, honestly looks like most the cells in battery 1 dropped early today slightly, then came back up a few minutes ago.. but battery 2 looks like it has just fallen over time... interesting. (I see there are 2 matching rows on battery 2, this may be a mistake) I will continue monitoring over time..

[Davydd]

Originally Posted by markopolo

I don't think David knows how much capacity was lost over the 6 years. If he does know then I don't think he has shared that info on the forum. It would be very useful to know for sure. Did they lose 1%, 5% 15% ? ? ?
.

Marko, if you had read the Advanced RV white paper on lithium ion batteries I’ve linked here a few times you would know there would be no apparent drop off in how the handle battery management They use the upper 80% of the battery capacity and never let you go below 20% without recharging. So yes, I don’t know nor did I care but it was not over 20% on apparent observation after 6 years and 95.000 miles of van use. ARV probably has more bells and whistles safeguards than any other upfitter to keep you from abusing your batteries yet no else seems to be concerned.

Heat is the bigger culprit. The Technomadia couple in a converted bus RV had some of the first lithium ion brand batteries (but an older generation) I had in my first ARV and they abused them terribly over some 4 years storing in Phoenix outdoor on asphalt in the summer and did report 20% loss. I doubt they had any cold weather experience. Given that lithium ion batteries have the capacity of over 2,000 cycles, I doubt you would need to be concerned. I didn’t for 6 years. I calculated with my normal use the cycles would get me more over 20 years. Now that is not a concern at my age.

If you read other papers it is a no no to charge to 100%. That’s a lab fallacy of optimizing but not a practical consideration. I charge to 100% every day on the road. It can’t be helped as I recharge at night’s stay in about an hour driving.

[Davydd]

Originally Posted by @Michael

Correct - you would not want to remove the batteries just because of the cold if you can keep them from charging when below freezing, and keep them going under -4F when not charging.

Correct. All you would have to do is charge them up and then disconnect the batteries in place to prevent charging from solar our occasional driving in cold weather. At -5 it would probably not be a concern if that is the temporary morning cold temperature and rising during the day. Connected batteries have their own internal heat and batteries inside a van cabin probably have an temperature above ambient. So you could probably leave them connected if you warm the cabin up before driving. Of course you could drive if you have disconnected batteries you just won’t have use of your electrical conveniences of the RV portion. I don’t know how other upfitters handle batteries but mine is just a switch to disconnect or reconnect.

[Lysergeon]

Update after another day of watching the cells... looks like they are pretty stable, battery 2 seems to be very slowly dropping voltage... do you think this is a sign of a permanent loss? and why only on the 1 battery? while the first battery seems to fluctuate up and down...

Any other thoughts on this?

[markopolo]

Was late afternoon on the 20th cooler than at noon?

The system seems to be maintained at approximately 13.5V. Perhaps thought to be not too bad until you see what can happen at the individual cell voltages.

B2 Cell 1 @ 3.501
B1 Cell 3 @ 3.509

They're high IMO. 3.501*4 or 3.509*4 is over 14V to put it into context. Few would think 14V is acceptable as a standby or storage voltage but that's what's happening here to those two cells.

You have a distinct advantage over those with LFP batteries that can't see individual cell voltages in that you'll be able to see the effect of changes in charging strategy. You may find that charging at 13.8V or 14.0 rather than PD's 14.6V keeps the cells in better balance.

[booster]

All of this is very interesting, and I think sometimes a bit confusing because some of what we heard in the past is now kind of being changed on the fly. IIRC correctly, ARV has historically limited SOC on both the top and bottom, for instance. 100% on the meter means really nothing about actual SOC as the meters can be set to read at 100% wherever you want very easily in most cases. This is true for lithium or other styles of batteries.


I also think that it is getting more and more futile to rehash what battery preserving strategies are needed/desirable/waste of time/harmful until we get some actual capacity testing over time. Without that it is virtually impossible, I think, to determine what is really going on with actual battery degradation over time. We have seen similar in past discussions with other battery types also, so this is not a new idea or necessity at all. Sure, lithium should last a long time so even if they degrade it may not be an issue for some people, but it also may be an issue for those that are using all their capacity (whatever it is compared to rated) regularly so they can't spare much loss at all. Those same high % users would also certainly benefit from accurate actual information on what helps preserve batteries in that if we knew just how much top and bottom space is needed, if any is, they may be able to use more of the battery capacity without any penalty for instance.

[Winston]

We have a slightly different and we believe simpler approach to this issue.

We don’t worry about whether we’re in “standby” or “storage”. Instead, we ask ourselves: “At what State-Of-Charge” do we want to maintain our lithium batteries, essentially, forever?” (Yes, we concede, that were we really to put our batteries into long-term storage we might pick a number like 50%.) But since our batteries get used throughout the year, we’ve chosen an SoC of 80%. Eighty-percent is a compromise between full 100% charge (which some contend is detrimental to the well-being of the batteries) and, say, that 50% storage number (which leaves too much battery capacity ‘unavailable’).

There are two occasions when we run our batteries to 100% full charge: 1) to balance the pack; and, 2) when we expect to be off ‘shore and solar power’ for an extended period of time and desire the full capacity of the pack.

To ascertain what “80% SoC” is, we charge our pack fully; discharge it by 20%, then wait 12 hours. During this 12 hour period - ALL charging and discharging of the pack is terminated. We then measure the voltage of the battery pack: 13.36 volts in our case. This becomes the operating voltage of our system (but, as our MagnaSine combo inverter/charger doesn’t deal in 1/100th of a volt, we round to 13.4 volts).

Now, forget Bulk, Absorb, and Float. Forget ‘charging’. Treat your charger/converter not as a charger/converter, but as a power supply. This can be done by switching your charger to the Constant Voltage mode (alas, not all chargers have this mode) and setting that constant voltage to 13.36 or, in our case, 13.4 volts. Plug your charger (now power supply) into shore power. Let it sit there for the six months you are lounging in the southwest’s winter warmth.

Are you “floating” your lithium pack? Are you damaging your lithium pack? Should you disconnect your lithium pack? No. No. And, No.

Here’s a rule of electrical engineering. If you connect a 13.4 volt power supply to a battery whose resting voltage is 13.4 volts (80% SoC), NOTHING HAPPENS. No current flows to your battery. No current flows from you battery. In short, your battery doesn’t know the power supply is connected! If your battery doesn’t know the power supply is connected, how can this be called “floating” . . . or, in any event, how can you damage a battery by connecting that which the battery doesn’t even know is there?

The beauty of this approach is . . . when you do connect a 12 volt load to the system, the power being delivered to that load is from the power supply. And, to the extent that the battery does supply some of the required load energy, the power supply will ‘replenish’ this lost energy (sometimes called ‘recharging’) without any human intervention.

If your Progressive Dynamics ‘charger’ doesn’t have a Constant Voltage mode, you may be able to simulate it by finding a charging profile in which the final resting voltage of the charger (the float voltage) is the desired 13.4 (or whatever voltage you select as your chosen State of Charge).