Lithium batteries - true longitudinal capacity profiles?

[InterBlog]

This is a cross-post from a thread I published on Air Forums because that is where my husband and I started our lithium conversations back in the day. But the considerations I describe below really apply to Class Bs generally, so I’m placing this content here as well, and I am curious as to what other early adopters are now discovering about their own lithium systems.

***

TL;DR = three takeaways in the image below.

Unpacking = as follows:

I’m reporting back on longitudinal performance of our lithium battery system which pre-dates most of those in operation today and thus provides a valuable real-world data point. My husband is an engineer and we were early adopters, with him designing and installing our customized system to dovetail into the available space in our 2007 Airstream Interstate van.

Back when we did this work, there were no off-the-shelf options for consumers who wanted lithium-based house battery systems. There was the well-known indie installer nicknamed Lewster and precious few others who were doing installs commercially, but most systems were built by skilled DIYers like ourselves.

At that time, the concerns of the installer community were limited to the following:

(1) How to design the system to prevent it from inadvertently charging in below-freezing temperatures, which would destroy the lithium cells.

(2) How to secure the lithium cells in the van so that they would not get damaged and start a fire in a crash.

(3) How many cycles the manufacturers were representing in the lifespan of lithium cells (acceptable losses were anticipated after a few thousand charging cycles over about a decade of use).

And guess what?? As is often the case with bleeding-edge technology, the factor that NOBODY was talking about turns out to be the thing that is actually driving this bus: time-dependent degradation that may or may not be exacerbated by climatic factors (especially heat) and which has little or nothing to do with “cycles”.

And why might that oversight have occurred? Because back when they started selling us this stuff, I suspect that manufacturers did not have 5+ year performance data. These battery products were all new. The best they could do was report cycle data. They can bench-test cycles, but in the rush to market, they can’t bench-test Father Time.

The challenges with my take-aways in the image below are obvious. Vanners typically don’t have the space to build their systems 50% larger than their calculated needs - we certainly don’t, with our battery cells tucked under our closet floor.

Plus at this point, we don’t even know how bad time-related degradation is going to get. Will it decelerate? Is it better to build systems larger at the outset, or should we simply plan to replace a smaller system in-kind around the 5-year mark because performance is just going to keep getting worse?

We suspect that a heat impact may be amplifying our time-related losses. Last night, my husband was web-chatting with Dacian Todea who designed and produced the Electrodacus BMS that we have been using since the outset of our lithium battery adventures. Dacian installed the same brand of “premium” batteries that we did, and he reported a 22% useable capacity loss in approximately the same period of time, vs. our 31%. But we live in one of the hottest metro areas of the country whereas he lives in Saskatchewan Canada, so we may be seeing an acceleration effect.

Many questions, few answers at this point. As for the unscheduled financial OUCH, I look at the bright side, which some of you techies might have snapped to before even getting to this paragraph:

The jury is still out on how badly time-dependent degradation affects lithium iron phosphate batteries in automotive applications generally. We don’t yet know what the longitudinal performance profiles will look like for the newest generations of hybrid passenger cars and EVs (e.g., Tesla did not begin mainstream production until 2018 - prior to that, it was a niche product with a very long wait list). My gasoline-only Toyota Sienna is now 12 years old with 135,000 miles on it, and I’ve been weighing when to buy a new one, having almost pulled the trigger a couple of times recently. But all Siennas are hybrids at this point, and there is NO WAY I am going to purchase ANY car with LiFePO4 components until I have a much better understanding of this emerging situation. So we may be sucking unexpected financial wind on our Class B lithium battery, but I feel like I just dodged a major bullet by having this come to my awareness now, before I spent far more money on it in the form of a new daily driver. Whew.

I encourage people to post additional examples of this phenomenon in this thread as we go forward.

As an aside, forum long-timers may have wondered why after 9 years of Class B ownership with a premium lithium system I was suddenly spending so much time and energy rehabbing our propane generator. Now you know the Paul Harvey rest of the story - because we knew that our lithium battery was failing and could no longer keep up with our energy needs. We just didn’t have time to perform a capacity test and quantify that degradation until yesterday.

[booster]

I have considered the whole lithium battery thing the "wild west" of batteries with every person for themselves since the beginning.


I suspect a lot of what we know now was known 5 years ago deep in the development labs, but that doesn't sell batteries. The marketing people got a hold of it and made all the wonderful claims to make the lithium seem economically feasible.


Consider the following, based on memory at this point, of what they claimed.


* You can use 100% of the capacity all the time and not cause shortening of life


* There is a huge range of temps that are not a problem, like -40* to 130*F or some crazy thing, that don't affect life



* You can store them in very cold temps down to -40*F



* You can charge below freezing at lower amperages


* You should put a 14.7v constant voltage charger on them all the time to charge and hold "float".


* You will get 10,000 cycles even if you do all the above.


* You can charge at 5C rates regularly if you have that much power


* No balancing of batteries or cellls required


Current information seems to be trending heavily toward saying all of these things are not true, from what I have seen.


As to your set of batteries, without knowing what kind of use they saw hard to determine what might have happened, but I would guess lots of the above stuff was done and all will shorten life.


My guess would be the heat from where you live and possible from where they are located. Add to it probable deep discharges which now are leaning toward being even worse for lithium than lead acid in regards to life. Possible charging at too high a voltage. Possible storing when not at reduced SOC which is now said to be necessary.


For starters you may want to do a search for the cycle life vs DOD for LiFePO4 batteries. Most of them now look as bad or worse than the lead acid ones. Same with the temp vs life charts. Charge profiles, in particular leaving head and footspace on the cycle have changed a bunch, with most saying at least stay off the dogleg on top but preferably 5-10% short of full and at least 10% on the bottom, although even at 90% discharge you shorten life a bunch.


Balancing the cells has also come to the front lately, it appears, with many of the drop in doing "automatic cell balancing", often on every cycle. Of course they initiate the balancing at 14.4-14.6v in many of them so they also are saying to overcharge on every cycle, per the other new rules.


Wild west, it still is, I think.


Remember when they claimed 20 years of typical life while doing all the bad stuff listed above? It is starting to look like they will have similar life to the AGM batteries of 5-8 years, unless folks find ways to prevent the early degradation with changes in how they are used and cared for.

[InterBlog]

Originally Posted by booster

I …
…
(1) … Add to it probable deep discharges which now are leaning toward being even worse for lithium than lead acid in regards to life. Possible charging at too high a voltage. Possible storing when not at reduced SOC which is now said to be necessary.

…
(2) …It is starting to look like they will have similar life to the AGM batteries of 5-8 years, unless folks find ways to prevent the early degradation with changes in how they are used and cared for.

(1) None of those apply. Our lithium cells were well cared for and only lightly used, with the battery not being “overstuffed” with charge during storage. Dacian’s were even more lightly used as he reportedly took them out of service because he was testing other battery products over the years. In our case, yes, we have the inescapable heat, but our van spends almost all of its time under cover and when it’s not under cover, it’s mostly at northern latitudes which are nowhere near as hot. I’ve tried to minimize the heat extremes to which the battery is subjected, but we do live near the upper Texas coast and it’s hot here.

(2) At this point, I agree on the lifespan, but I’m not sure what can be done to maximize life, that we are not already doing.

[booster]

What is your charge profile and voltages?


How deep do you discharge them typically?

[Urlauber]

With the cheaper LFP batteries now costing around $270+tx for 100Ah, this may become less of an issue. Sure, it would be better to get more life out of them, but it's not like you're out a grand every time they need to be replaced.
That's cheaper than what the Trojan Grp 31 AGM batteries that are in my rig currently cost.
And they are still much smaller and lighter. I am sure over time they will get better too...

[InterBlog]

Originally Posted by Urlauber

With the cheaper LFP batteries now costing around $270+tx for 100Ah, this may become less of an issue. Sure, it would be better to get more life out of them, but it's not like you're out a grand every time they need to be replaced.
…
…

We have 300 Ah, so by that math, it’s $810 plus tax and shipping. So yeah, I’m out a grand every time they need to be replaced.

My husband has a set of preferred brands, and he calculates about $1,200.

[InterBlog]

Originally Posted by booster

What is your charge profile and voltages?


How deep do you discharge them typically?

Charging is almost entirely by solar, so it’s slow and gentle. My husband’s initial suspicion was a contribution to the capacity problem via solar panel aging and loss of efficiency, but the data did not show that. We have 3 of the Grape Solar high-efficiency panels that were favored by vanners for their roof fit but which were discontinued some years ago (I can’t remember the reason). They are standing up well.

We have never discharged below 20% (our Electrodacus BMS halts it). Typically we never go below 30% in practice. Once or twice, we got down to the cut-off value.

[booster]

Originally Posted by InterBlog

Charging is almost entirely by solar, so it’s slow and gentle. My husband’s initial suspicion was a contribution to the capacity problem via solar panel aging and loss of efficiency, but the data did not show that. We have 3 of the Grape Solar high-efficiency panels that were favored by vanners for their roof fit but which were discontinued some years ago (I can’t remember the reason). They are standing up well.

We have never discharged below 20% (our Electrodacus BMS halts it). Typically we never go below 30% in practice. Once or twice, we got down to the cut-off value.

Slow charging doesn't seem to be an issue from what I have read, and cycling in the middle of SOC is said to be a good thing. We have the same panels and had no issues with ours either. What voltages do you have set in the solar? Do you have a battery monitor on the system? Some solar controllers from that era put a full charge of like 4 hours on the batteries every day as they run on timers and don't check starting voltage to see if a charge is needed, and that can be a real issue when the van is sitting, stored, with full batteries and in the sun.



The going to 20% SOC will reduce life by a lot according to a growing number of sources I found, but you should still get something like 2000 cycles out of them. Are you also leaving some space at the top of the charge by stopping changing at 13.6-13.8v?


Of growing concern to me, at least with the drop in batteries, is the balance of the cells going off over time if you don't have a balancer, preferably an active one. Do you have a balancer on them?

[Urlauber]

Originally Posted by InterBlog

We have 300 Ah, so by that math, it’s $810 plus tax and shipping. So yeah, I’m out a grand every time they need to be replaced.

My husband has a set of preferred brands, and he calculates about $1,200.

Yes, of course, and if you have 800Ah it will scale accordingly. My point is that good deep cycle AGM batteries can be just as or more expensive than LFP batteries these days.

And, of course, it would be ideal if these would last 10+ years and 10000 cycles, but this reminds me of early LEDs which also came with incredible promises of longevity. Flashing streetlights tell otherwise.

[hbn7hj]

You guys are looking for longevity I’m looking for a 200 amp charge rate from an AC charger. Got a few more ideas to try this fall. I’ll probably push it till I start a fire.

Just a comment.

[booster]

Originally Posted by hbn7hj

You guys are looking for longevity I’m looking for a 200 amp charge rate from an AC charger. Got a few more ideas to try this fall. I’ll probably push it till I start a fire.

Just a comment.

I think most that look for that much shore power charging are using two 100 amp chargers in parallel. I have seen several that listed that they claim can be ganged to increase charge rate. I don't recall the brands, but I know it was more than one I have seen.

[hbn7hj]

Originally Posted by booster

I think most that look for that much shore power charging are using two 100 amp chargers in parallel. I have seen several that listed that they claim can be ganged to increase charge rate. I don't recall the brands, but I know it was more than one I have seen.

Iota has one and I have it. That is where I am headed this fall. Maybe ditch all the smaller smart chargers and get a second.

[Boxster1971]

InterBlog - assume you have read and watched the info on lithium RV batteries by Technomania. In case you or other have not here are some links to their useful info:

https://www.technomadia.com/2015/02/...attery-update/

https://youtu.be/0j0zcRXTDRk

[Urlauber]

Good site/blog. Heat, and keeping them constantly charged/charging, may be two big detriments to the LFP life span.

The charging thing is easy to manage/avoid, heat a bit more difficult. Many place their batteries inside the camper which may actually exacerbate the situation if the vehicle is parked outside/in the sun. Vacationing in the Southwest or South in Summer, it can be very difficult to keep things cool.

[@Michael]

Originally Posted by Boxster1971

InterBlog - assume you have read and watched the info on lithium RV batteries by Technomania. In case you or other have not here are some links to their useful info:

https://www.technomadia.com/2015/02/...attery-update/

https://youtu.be/0j0zcRXTDRk

They ended up getting 8 yrs out of them, but at reduced capacity (75%).

https://www.technomadia.com/2020/06/...rs-of-lifepo4/

[Boxster1971]

Originally Posted by @Michael

They ended up getting 8 yrs out of them, but at reduced capacity (75%).

https://www.technomadia.com/2020/06/...rs-of-lifepo4/

Yes - but they died in storage due to power outage and LED on the balancing board. They would have probably lasted a lot longer if they had not been fully discharged in storage.

As they said in post:
"We fully anticipate that had we not run into the storage power outage situation, we would have gotten the anticipated 10+ years out of pack that we had anticipated in our original cost analysis."

I also found the disclaimer at end of their post a joke:

"Disclaimer: While Battle Born provided our batteries for both the bus and boat, we have received no compensation for writing this post. . ."

What? They don't think two complete battery systems provided free is compensation?

[booster]

The original link given was for their 3.5 year update and they were already down to 75%. Per the 80% worn out limit that is commonly applied to AGM batteries, they were already worn out at that point.


I didn't see anywhere what the charge profile was, but in that era I would expect it to be 14.4v-14.7 absorption and 13.5-13.8 float as that was the common recommendation then. That in itself may have damaged them.


There was also no mention of discharge depth that was often claimed to be 100% then.

[Davydd]

Originally Posted by Boxster1971

InterBlog - assume you have read and watched the info on lithium RV batteries by Technomania. In case you or other have not here are some links to their useful info:

https://www.technomadia.com/2015/02/...attery-update/

https://youtu.be/0j0zcRXTDRk

The Technomadia couple doesn't explain thoroughly the 6 months storage over the summer was in Phoenix on asphalt pavement. it might have not been as hot as this year but it still got as hot over 104 degrees and the asphalt as we know gets hotter.

Their experience is a decade old. I had the same batteries for 6 years since 2014 not experiencing what they went through.

I think they are on a boat now.

BTW, as I have mentioned numerous times I try to travel chasing 70 degree weather seasonally or location. Mostly successfully, but I have been in freezing weather down to -15 degrees overnight and above 90 degrees a few times. I store in a garage at 50 degrees minimum and I checked recently that the garage topped out at 80 degrees on a 96 degree day outside.

[RossWilliams]

I think the takeaways apply to RV batteries in general. Manufacturers provide theoretical numbers based on hypothetical situations. Real life is going to be different. Battery life cycle and AH ratings are clear examples of this. They are useful for comparison, but not really for real world use.

Sizing your system substantially larger than the expected need is desirable if you are looking at permanent long term use. Perhaps not if you anticipate selling the RV long before it wears out. Early adopters of technology are always going to find that information on long term considerations was not available. That's part of being a "beta tester."

The same applies to new uses of old technology. The increased use of electricity rather than propane may have some long term effects on battery capacity in general. Relying on batteries to boondock running a microwave, stovetop, refrigerator, air conditioner and media center is a relatively new phenomena. So we don't really know.

It is helpful to recognize that cost and other comparisons of lithium to lead acid batteries are still relying on limited real world experience.

[W9TR]

This is good info, thanks all for posting. I wonder how more recently manufactured LiPO4 batteries will fare.

I’ll note that the 50% AGM discharge limit doesn’t hold up factually, at least for the Trojan 31 series AGM batteries in our van.

Trojan states that 50% DOD gets you 1000 cycles while 80% DOD gets you 600 cycles, seemingly a big lifecycle drop. But that’s not taking into account the extra energy you get by discharging to 20%.

For a 100 AH battery :
50% DOD gets you 50 AH x 1000 cycles = 50,000 AH lifetime.
80% SOD gets you 80 AH x 600 cycles = 48,000 AH lifetime.

So while I wait for my AGM’s to reach the end of their useful life (maybe longer than we own the van) I’ll discharge them to 20% when the need arises secure in the knowledge that I am doing no harm.