What happens to LFP batteries after their 3500 cycles? - Page 1
Forum section: electronics / general

author: brucehoult
author_rank: Super Contributor
timestamp: June 17, 2025, 01:19:51 am
content: OK, so various manufacturers say that after N cycles (N = 3000, 3500, 4000) their LFP battery has 80% of the original capacity.What happens after that at, say, 2N cycles? 64% (0.8*0.60%? Dead? And at 3N cycles 50% (51.2)? Or dead?Also, if the manufacturer has got these numbers from actual testing then presumably that's been done at 1 C (or more) in order to test 3000-4000 full charge/discharge cycles in under a year.I've seen suggestions that if you're charging (especially) and discharging at 0.1 C or 0.2 C, as you generally are in a solar power setting rather than an EV, then you might get considerably less degradation. Opinions? Data?

author: 5U4GB
author_rank: Super Contributor
timestamp: June 17, 2025, 07:01:00 am
content: Charging at < 1C for solar depends on your charge controller, only some support it. An ongoing gripe about Enphase for example is that you can't limit the charge rate, it always charges at whatever maximum rate it can draw power till it reaches 100%, then sits there wasting the rest of the charging time.

author: brucehoult
author_rank: Super Contributor
timestamp: June 17, 2025, 08:23:35 am
content: Quote from: 5U4GB on June 17, 2025, 07:01:00 amYou tend to not have to DO anything to get < 1C because if your solar array is charging your battery in 1 hour not 5+ hours then you've either bought waaaaay too many panels or waaaay too little battery.And if you're charging for 8 hours a day then discharging for 16 hours then that's obviously maximum 0.06 C on the discharge side.

author: rteodor
author_rank: Frequent Contributor
timestamp: June 17, 2025, 09:30:31 am
content: Quote from: brucehoult on June 17, 2025, 01:19:51 amOpinion, not data (nobody knows for sure I think because LFP is so new): degradation is much more abrupt after specified 80% (or 70%) point. At 2N its more like 20% of initial capacity.Cycle number may not matter much in ESS anyway, because they will start to degrade chemically after 10...15 years. This happens even if they are not used. We suspect that by observing other types of Li-Ion's. After 10 years many LFP's used lightly in ESS might not have been used to even half of those 3500 cycles (calculated in cycled Ah).One thing I heard about to significantly improve the cycle number/lifetime is to have proper compression at the very first few cycles. Initial compression would determine residual gases from manufacturing process to be vented out instead of being incorporated chemically. If cycled without initial compression then gases are taken in chemically and reduce the cycle count and lifetime.

author: brucehoult
author_rank: Super Contributor
timestamp: June 17, 2025, 10:42:15 am
content: Physical compression / pressure on cells?I'm certainly not going to be able to do that with the cells deep inside the Pecron E3600LFP that I should be picking up from the local courier depot tomorrow!I can follow any recommended initial charge/discharge treatment, but disassembling it is right out!The credible-looking suggestions I've seen are to give a good solid initial 100% charge or two, to get the cells equalised. And at least one full discharge (to cutoff) to calibrate things. It does have display of individual cell voltages for the unit itself, and up to four attached 3072Wh expansion batteries. (photo from internet)

author: rteodor
author_rank: Frequent Contributor
timestamp: June 17, 2025, 11:42:12 am
content: Quote from: brucehoult on June 17, 2025, 10:42:15 amIt its closed then its closed. Nothing to do with it. It probably does not have compression but then its 'maintenance free'.The screenshot is just an example of the spec (with compression) for the LF280K cells that started to appear about 3 years ago:

author: brucehoult
author_rank: Super Contributor
timestamp: June 17, 2025, 12:06:17 pm
content: Quote from: rteodor on June 17, 2025, 11:42:12 amOh I see. Sold as individual 3.2V cells!https://www.nzlithium.co.nz/product-page/eve-lf280k-grade-a-1Interestingly the 280ah cell is sold for NZ$280 and the 314ah cell is sold for NZ$315.

author: 5U4GB
author_rank: Super Contributor
timestamp: June 17, 2025, 12:54:42 pm
content: Quote from: brucehoult on June 17, 2025, 08:23:35 amThis is charging it from free surplus power provided by the power company at night to encourage load-shifting. So instead of charging at a low rate spread across the free-power interval it charges at the maximum rate possible until it reaches 100% charge, then stops and sits idle.

author: brucehoult
author_rank: Super Contributor
timestamp: June 17, 2025, 01:51:42 pm
content: Quote from: 5U4GB on June 17, 2025, 12:54:42 pmOh!You'd said "Charging at < 1C for solar depends on your charge controller, only some support it." so I assumed you meant charging from solar panels.My first venture into home battery stuff starts, hopefully, tomorrow when I pick up a Pecron E3600LFP from my local courier depot. Well, I hope tomorrow, it shipped from Auckland at 1 PM so should be there overnight.That has a 3072Wh battery (with the ability to expand to 15kWh) and has settings to limit AC charging rate to 10%, 20%, 30% ... %80%, 90%, 100%. I'm intending to start using it for load-shifting immediately, and yes charging at a slow rate from 11 PM to 7 AM. It's not FREE power here, but it's half the price of power from 7-9 AM and 5-9 PM.It's got two 1200W MPPT controllers and I'm drawing up plans for how to go about getting some panels and mounting them and wiring them up etc, but that's not particularly urgent and I might wait until nearer to spring. We only get 9h45m of daylight at the moment, the sun never gets higher than 31º vs 14h30m of daylight and 78º altitude at noon in December when it's above 30º altitude from 8:45 AM until 6 PM. It's also very often overcast and raining at the moment. Well, that would be a good test, for sure...You can also set a battery charge percentage limit for charging from AC, so I could for example put enough charge in overnight to get through the morning peak, but leave capacity for solar cells to top it up.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 17, 2025, 06:45:30 pm
content: Usually, aging slows down: so if it takes N cycles to reach 80%, after 2N cycles youusuallyhave more than 60% of capacity left. Maybe 65-70% or so - if all goes well.But such analysis is risky; unit-to-unit variation is large, and sometimes a small hidden defect escalates to quicker failure. Which can even happen well before the "guaranteed" number of cycles, or it can happen after it.Also, don't forget that increasing ESR is another aging mechanism. It depends on your use case which one is limiting, capacity drop or ESR rise. If you need large discharge/charge current, then ESR rise "shows as" a capacity drop, even if you get decent capacity with lower current. This is because you have to stop discharging when you hit the low voltage limit.Cycle life is also a complex function of maximum SoC, minimum SoC, charging temperature, charging current... Specifically, combinations of high charge currents near full SoC atlowtemperature are harmful. Long cycles are more harmful: a 80% cycle does more damage than two 40% cycles. 100%-80%-100% cycle is more harmful than 60%-40%-60% cycle... And so on. What's worst, the amount of research needed to properly characterized all of this is years behind with the huge number of actual product lines. Even manufactures themselves do not have full idea of the lifetime mechanisms of their cells. You can spend ayearworth of your time to characterize one product, and then that product is out of market in a few years, and something similar, but not exactly the same, is available then.And almost no one does 100%-0% cycles all day long, yet that's what done when testing the batteries. Therefore, in real use batteries often overdeliver: last longer than promised. And yet, some semi-dodgy manufacturer could well take that into account, and "oversell" the battery to compensate; maybe their test showed the battery degrades to 80% capacity after 2500 100%-0% cycles, and they sell it as 6000-cycle battery knowing the end user would rarely do full cycles.

author: thm_w
author_rank: Super Contributor
timestamp: June 17, 2025, 10:49:24 pm
content: You can see some measurements here:https://www.researchgate.net/figure/Discharge-capacity-retention-for-all-LFP-blue-NMC-black-and-NCA-red-cells_fig1_343593077https://physicsworld.com/a/degradation-of-commercial-lithium-ion-cells-beyond-80-capacity/Most of the LFP shown there seem to have a fairly linear dropoff.But there is a large variance in who manufactured the cell, what composition, etc. Its not guaranteed what you will get. And real world results might not be the same as in the lab (eg lifepo4 lab calendar aging tests were much worse than real world tesla LFP pack aging).Still, I'm sure by the time a decent brand lifepo4 has significantly degraded, costs will have dropped and sodium ion cells might be more readily available.

author: temperance
author_rank: Super Contributor
timestamp: June 17, 2025, 11:59:33 pm
content: There is indeed more to battery life than the number of cycles. Batteries degrade over time as well, for various reasons. The search term you are after is called "calendar aging".https://www.sciencedirect.com/science/article/pii/S2542435124005105https://www.okrasolar.com/blog/a-better-way-to-estimate-battery-lifetimeThe real problem is that you can't just perform a simple test when evaluating new batteries, and you have to trust the manufacturer.EDIT: For a customer, I have around 200 LFP batteries 12V/20Ah installed all over EU made out of individual 10 Ah cells. They are cycled almost every day and discharge has been limited to 80%. The packs all have the usual suspects on boards like over discharge, overcharge and overcurrent protection. The charger has active cell balancing. But after 12 years, all those batteries show the same problem. Inconsistent capacity readings and internal leakage current on the order of 100...350 mA.Good luck to those buying second hand electric cars...EDIT2:QuoteIs there a reason why you think sodium ion cells might perform better?

author: thm_w
author_rank: Super Contributor
timestamp: June 18, 2025, 12:44:01 am
content: Quote from: temperance on June 17, 2025, 11:59:33 pmSecond hand LFP cars are great. 100,000km is only 300-400 charge cycles, so the capacity is not even close to being degraded, they can often still be at >90% capacity.QuoteThe current spec is not any better, but, I'm expecting the cost to drop so much that you'll end up with double or triple the capacity, meaning even if the cycle life is the same it would still effectively last longer (where weight is not a concern).There are also 6,000-13,000+ cycle estimates in the lab from various improvements, if we get them who knows:https://www.sciencedirect.com/science/article/abs/pii/S2211285524006554

author: 5U4GB
author_rank: Super Contributor
timestamp: June 18, 2025, 09:08:14 am
content: Quote from: brucehoult on June 17, 2025, 01:51:42 pmNah, I meant topping up your batteries for free overnight on one of the EV power plans. I get the feeling, from Enphase forum discussions, that this isn't done much in the US so there's no concept of needing to spread the charging over a given time interval, the assumption is that the power is coming from the naturally self-limiting solar panels rather than the (effectively) limitless grid.QuoteThat's still better than Enphase's "tell someone who cares" response to charge control, but what you really want is a way to say "you have X hours to get to 100% charge, set the rate appropriately". If you have something like modbus control you can presumably set this yourself based on the charge level, so an optimum-rate charge for most of the time interval and then a slow top-up for the final 10%.

author: David Hess
author_rank: Super Contributor
timestamp: June 18, 2025, 10:53:27 am
content: Quote from: temperance on June 17, 2025, 11:59:33 pmWe are starting to see that in car auctions, but worse for hybrids.Many hybrids are completely disabled once the battery fails, and the batteries are only lasting half of the specified lifetime at most, while being out of production. The only replacement option is to either find a used battery which has not failed from another vehicle, or maybe there is a third party which can rebuild it. Cost of the battery replacement is so high that the vehicle's only value is for scrap, so these vehicles are just sitting on the auction lots.It is hard to believe that the batteries are not lasting as long as the car manufacturers said they would.

author: brucehoult
author_rank: Super Contributor
timestamp: June 18, 2025, 11:09:01 am
content: Quote from: David Hess on June 18, 2025, 10:53:27 amThat doesn't make any sense.This time last year I hired a 2012 Prius with nearly 300,000 km on it for 8 weeks. I'm sure it was the original battery and it worked fine -- it would drive several km at 50 or 60 km/h without starting the engine.Prius only has about a 2kWh battery, and uses about 1kWh of the capacity. 2kWh LFP batteries are now about $500. I don't know how much a bare generic NiMH battery costs but I suppose not much more or different.I see prices for replacement batteries between $1200 and $1500 here, with guarantee:https://www.besthybridbatteries.com/categories/hybrid-batteries-by-make/toyota/priusI also see companies offering LFP and even Sodium-Ion upgrades for old Prius, but at the higher cost it may not be worth it on an older near EOL chassis. Putting in a replacement NiMH should be enough to keep one going until it falls apart.By now there are probably a ton of crashed Prius' with undamaged batteries.

author: shapirus
author_rank: Super Contributor
timestamp: June 18, 2025, 11:12:41 am
content: Quote from: brucehoult on June 17, 2025, 10:42:15 amThis is an interesting topic. I once got interested and tried to search for further information only to find that there is no reliable information on this. Yes the datasheets specify that the cells were compressed in particular tests, but they don't say what would happen if the cells weren't compressed.The most plausible information (which looked more like opinions) was that compression is required to avoid cell deformation due to possible buildup of gases at high (>0.5C) rates of charge (and/or discharge, I'm not sure).It'd be interesting to hear from those who know more. Specifically, what the reasoning behind compressing cells might be, which will allow to understand when it is required and when it doesn't matter.

author: temperance
author_rank: Super Contributor
timestamp: June 18, 2025, 12:47:20 pm
content: QuoteThat's indeed interesting because manufacturers of Lithium pouch cells recommend leaving some room for expansion. At least that's what a manufacturer told me about 15 years ago.

author: Ice-Tea
author_rank: Super Contributor
timestamp: June 18, 2025, 01:15:01 pm
content: Quote from: brucehoult on June 17, 2025, 12:06:17 pmYou can buy them for about half that.

author: brucehoult
author_rank: Super Contributor
timestamp: June 18, 2025, 01:28:36 pm
content: Quote from: Ice-Tea on June 18, 2025, 01:15:01 pmIt's funny how people who say such things seldom give a URL.And, no, EU or USA does not count.

author: shapirus
author_rank: Super Contributor
timestamp: June 18, 2025, 01:44:16 pm
content: Quote from: brucehoult on June 18, 2025, 01:28:36 pmThen we can't do much other than tease you

author: David Hess
author_rank: Super Contributor
timestamp: June 18, 2025, 07:34:12 pm
content: Quote from: brucehoult on June 18, 2025, 11:09:01 amThere were American made hybrid luxury SUVs, Cadillac I think. I saw an entire row in the lot.

author: brucehoult
author_rank: Super Contributor
timestamp: June 19, 2025, 12:36:07 am
content: Guess that's a Cadillac problem, not a hybrid problem?

author: David Hess
author_rank: Super Contributor
timestamp: June 19, 2025, 11:51:32 am
content: Quote from: brucehoult on June 19, 2025, 12:36:07 amThey were not the only ones. In theory a software change would at least allow them to operate with a bad battery like some other hybrids, but that is not happening.Modern vehicles have too many modules that are either unreliable or expensive, or not even available for replacement, like for instance the transmission on a Prius, or the battery in a hybrid. It is as if Apple Computer was making cars; if something breaks, throw it away, and buy a new one.

author: brucehoult
author_rank: Super Contributor
timestamp: June 19, 2025, 02:33:47 pm
content: Quote from: David Hess on June 19, 2025, 11:51:32 amWhich one of those is the transmission on a Prius?The transmission, such as it is, is essentially functionally a diff in reverse with the prop shaft driving the wheels, one axle connected to the engine, and the other to Motor/generator 1 (except that the gear ratios to each "axle" are different. The actual implementation of the planetary gears is a bit different but it's cheap, robust, and long-lived.

author: David Hess
author_rank: Super Contributor
timestamp: June 19, 2025, 04:32:47 pm
content: Quote from: brucehoult on June 19, 2025, 02:33:47 pmExpensive, like a $24,000 price to replace one, and they are not meant to be serviced.

author: brucehoult
author_rank: Super Contributor
timestamp: June 19, 2025, 04:58:43 pm
content: Quote from: David Hess on June 19, 2025, 04:32:47 pmDo you have evidence for that?Both a google search and asking Grok indicate a maximum price in the low single digit thousands for a new replacement, with lower prices for used or reconditioned units.For example this dealer says "The cost of a new Toyota Prius transmission could be over $3,500 depending on the vehicle, yet, transmission services such as fluid changes and a transmission fluid flush are considerably less expensive, in some cases costing less than $150"https://www.stevinsontoyotawest.com/toyota-prius-transmission.htmThat seems entirely reasonable for something that lasts typically 250,000 to 300,000 km or even 500,000 km with a gentle driver and regular maintenance -- in many cases the life of the car.

author: David Hess
author_rank: Super Contributor
timestamp: June 19, 2025, 06:33:30 pm
content: Quote from: brucehoult on June 19, 2025, 04:58:43 pmTestimony from someone who went through it and gave up. It was part of a documentary. I assume it was an older model, but it did not have nearly that many miles on it.

author: thm_w
author_rank: Super Contributor
timestamp: June 19, 2025, 08:57:00 pm
content: Thats probably a dealer quote, dealers are in it to make most of their money on repairs and maintenance.They also would never offer used parts, if you have a 10 year old car it generally doesn't make sense to put in a new part.Its not unheard of for BMW dealerships to charge $300-400 to change a cabin air filter.

author: David Hess
author_rank: Super Contributor
timestamp: June 19, 2025, 10:54:07 pm
content: Quote from: thm_w on June 19, 2025, 08:57:00 pmIt probably was a dealer quote, and a replacement transmission module from Toyota. I think it was Carwizard who mentioned it as an example of when putting money into repairs is not worth it. BMW seems to be particularly bad because modules are only in production for the most limited time and must be programmed.

author: langwadt
author_rank: Super Contributor
timestamp: June 20, 2025, 12:02:43 am
content: Quote from: David Hess on June 19, 2025, 10:54:07 pmin EU they have to make spares available for something like 10 years minimum, I'm guessing the insurance companies had a say in that.I remember when Fisker went bankrupt, all the cars became instantly uninsurable except for liability, insurance companies don't want to insure an expensivecar that would have to be totaled for even minor damage because there are no parts to repair it

author: brucehoult
author_rank: Super Contributor
timestamp: June 20, 2025, 01:41:07 am
content: Quote from: David Hess on June 19, 2025, 10:54:07 pmThere is a lot of nonsense talked about when repairs are or are not worth it, even from professionals.- it's not worth spending $2000 to repair a car that is only "worth" $1000. Rubbish. If that repair gets you another 100,000 km instead of going out and paying far more for a new car then it's absolutely worth it- it's still only worth $1000 after you spend the $2000. Maybe that's all you could sell it for, but you're not planning to sell it, you're going to use it, right?- you could buy another one for $1000 that doesn't need the repair. Well, it doesn't need a repair *now*. With someone else's car you have no idea of the history and maintenance and what is likely to go wrong soon. You have much more information about your own vehicle.The thing you have to look at is how much your paid-for vehicle is costing you per year or per km, on average. Compare that to the finance cost (loan, or not being able to invest that money) for a new(er) vehicle.QuoteI have no problems getting replacement parts for my 1995 BMW R1100RT -- it turns 30 this year! A couple of years back I needed a new Hall-effect crankshaft position sensor assembly. The part of the wiring that lives inside the front engine cover has seen too much heat/cycling and the insulation had crumbled causing a short circuit. It wasn't even expensive, but just needed a couple of months to come from Europe. Pic below from when I picked it up after that repair.Unless they are exotic, older vehicles have a ready supply of used parts in good condition. For example a couple of years ago I reversed my 2008 Subaru Outback into a scaffolding pipe I didn't see at night. I was due to drive 1000 km home from another city two days later. I went in to a repair place at 10 AM and by 3 PM they'd found a replacement rear door / hatch, had it couriered across town, and fitted it and I was ready to go. The total cost was around US$500. In that time the only thing they couldn't do was paint it so I have a mismatched rear door. I can paint that any time I decide to but I haven't yet -- most people don't even notice the dark grey door is out of place on the red car. Two-tone costs more, right?You of course will notice, since I just pointed it out :-)One, day ...

author: brucehoult
author_rank: Super Contributor
timestamp: June 20, 2025, 01:43:21 am
content: Quote from: langwadt on June 20, 2025, 12:02:43 amI've never had any problem getting parts for 20-30 year old Toyota, Honda, Subaru, BMW. I haven't owned other brands to know.

author: 5U4GB
author_rank: Super Contributor
timestamp: June 20, 2025, 05:21:40 am
content: Quote from: David Hess on June 19, 2025, 10:54:07 pmThis is why you never go to an authorised BMW dealer who will look at the car, say "it's probably this", replace the entire thing when one small part if it may be faulty, and charge you $5,000 for the privilege. Two weeks later the fault will be back.An unauthorised BMW repair guy will say "yeah, known problem with that model and year when they started making them out of plastic rather than aluminium, I can swap it out for one from the 20 worth-more-as-spare-parts cars I have out the back, cost yer $200".

author: 5U4GB
author_rank: Super Contributor
timestamp: June 20, 2025, 06:41:51 am
content: Quote from: brucehoult on June 20, 2025, 01:41:07 amI think bikes (or at least repairs/part) are a very different thing to cars though, so you can't really compare them. See also my previous post about BMW's ill-advised foray into corners-cut cars which are now worth more as mobile collections of spare parts than as a (partly-functioning) vehicle.

author: David Hess
author_rank: Super Contributor
timestamp: June 20, 2025, 11:20:13 am
content: Quote from: brucehoult on June 20, 2025, 01:41:07 amThe problem is with newer vehicles. In the case of the BMW, the only source for various electronic modules was other cars of the same year, and the modules must be reprogrammed with the same ID. In the case I saw, I think it was the battery control module or something which because of placement is likely to get water or battery leakage inside. They managed to find one (!) available, and there is one (!) known guy who will rebuild and reprogram them.I was looking at changing the chassis control module on my 2002 pickup to add the original fog light controls, but the cost of the module and reprogramming could be almost $1000, with most of the cost being the reprogramming.Quote from: brucehoult on June 20, 2025, 01:41:07 amWhen I pulled my 2002 pickup out of 7 years of storage, it needed about $2000 worth of work for a broken spark plug (1) and various other minor issues, plus registration. The Blue Book value is maybe $3500, however in my particular case it is very low mileage so well worth it. My rusting out 1997 Nissan Sentra however was not even worth fixing or paying for storage.But what about a 5 or 10 year old modern vehicle which will require $30,000 dollars worth of repairs because the traction battery or hybrid transmission needs to be replaced? Or what about a water damaged BMW where most of the no-longer-produced electronic modules must be scavenged from other vehicles and reprogrammed? In the BMW example above, if that single battery control unit had not been available, there would have been nothing more to do.(1) I was not familiar enough with the engine at the time to trust doing the work myself.

author: brucehoult
author_rank: Super Contributor
timestamp: June 20, 2025, 11:38:57 am
content: Quote from: David Hess on June 20, 2025, 11:20:13 amAll the more reason to keep old things going, don't you think?Especially if you're going to die soon anyway. RELATIVELY soon, I mean ... historically I've used vehicles until they're 25 or 30 years old anyway, and I'm in my 60s. I bought that motorcycle when I was 32.

author: David Hess
author_rank: Super Contributor
timestamp: June 20, 2025, 12:49:58 pm
content: Quote from: brucehoult on June 20, 2025, 11:38:57 amWhich is what I am doing with my cream puff 2002 low mileage pickup, but I wonder what I will replace it with when the time comes. I am considering getting a similar pickup sans engine and rebuilding the whole thing with a Cummins R2.8, but adaptive cruise control and lane following in a newer vehicle are tempting.

author: brucehoult
author_rank: Super Contributor
timestamp: June 20, 2025, 01:06:42 pm
content: Quote from: David Hess on June 20, 2025, 12:49:58 pmMy 2008 Subaru has adaptive cruise control, automatic braking, and lane departure warning but not automatic steering. I think it's good to have *something* to do. Also conventional 5 speed automatic, not CVT. I owned a car with CVT the year I lived in the USA (2019) and to be honest the fuel economy wan't all that much better .. the difference could as easily be turbo vs NA.https://www.fuelly.com/car/subaru/outback/2008/brucehoult/1005227https://www.fuelly.com/car/subaru/outback/2017/brucehoult/912743The best tank MPG is only 2.5% different and the average 8% but the 2017 CVT car was almost entirely freeway driving, and in NZ it's basically zero freeway driving (I have to drive 130 km on twisty hilly 2-lane to get to one, while in CA I was 1 km from the freeway entrance.)

author: David Hess
author_rank: Super Contributor
timestamp: June 20, 2025, 09:44:58 pm
content: When I bought my pickup, I was only interested in manual transmissions, and that is still the case.