More interesting cycle life data

[zcskywire2]

In most solar installs, the batteries are rarely fully cycled in a day (Either real cycles or equivalent cycles). Furthermore, it is rare to charge or discharge at a full 1C. (I try to design a system to be charged at around .3C or less and never above .5C). Charging and discharging slower tends to wear the battery slower so you get more cycles or equivalent cycles out of it.

To add to this, center charging/discharging lifepso4 batteries, just as you would with solar will make them last longer. We center tested some cells at work. They were cycled at ~25-75 soc. They just refused to die, we got >12k cycles at a way more aggressive profile than most people would use. We ended the testing before the cells failed. The full up and down cells crapped out months earlier.

Id also be curious if you had any other information on the lifecycle testing of that Ganfeng cell that you could share.

 

[OffGridInTheCity]

I'm 18650 MNC lithium-ion chemistry. After 5 years I'm here on (infamous) Battery University chart with my oldest battery

and no detectable degradation. Nothing amazing yet... in another 5 years, at 3,000+ cycles, it will start to get interesting if things go that far. I would expect LifePo4 to do at least as well. (Can't believe 5 years have gone by since I started solar)

 

[sunsurfer]

nice strait line. If the line holds, they will be good well past 80%

 

[Sojourner1]

Yes. I (and others) have often pointed out that calendar aging is more likely to get you before cycle aging.

And if calender aging doesn't do it the hen pecking some do will get them eventually.
I guess the set and forget isn't good enough. ?

 

[wattmatters]

Whatever a cycle exactly is, they will last for a very long time when used as ESS for most home users.

No dispute, provided they are not subjected to extreme conditions and the BMS doesn't fail to protect them in a moment of need.

I agree, but that should be taken as an upper limit with calendar aging providing the lower limit.

Instead we get "cycles" which is a poorly defined term and of little use.

I think something akin to a car warranty makes more sense:
X% of capacity remains after Y kWh of throughput or Z years, whichever comes first.
Subject to being used within operating parameters.

 

[sunsurfer]

Would I be correct to assume that average ambient temps play a role in calendar aging?

 

[JRH]

I don't know if they were in a fixture or not. Sorry


I am not sure I am a zealot about it, but I agree. Even if the test used a fixture and you discount it down to 3000 cycles at 1C/1C.... the numbers are still big enough that cycle life should not be a concern. Something else will get you first so trying to extend cycle life has limited return on the effort.

My BMV712 , in the history tab ,on the BT page ,under “ total charge cycles “ is logging a cycle everytime you discharge below @50% and then recharge back up.
I tested it yesterday to see where it considers a cycle.…
sure enough it logged another cycle ,at 55% down..the same as when I did a 95% discharge ..but it doesn’t at lesser discharges Like 25 or 30 % ….
For whatever that means to anyone, that’s what it does…I really don’t care as I don’t think in decades anymore ,,,,I’m sorta pushing it if I think in years… but who knows.?

 

[sunshine_eggo]

Here is an interesting chart on Cycle Life:

View attachment 146496

Look at the charge and discharge rate. 1C for both and they still lasted over 4000 cycles before they hit 80%. In a typical solar installation, the charge and discharge rate won't be anywhere near that high. I can easily imagine a cycle life of 8000 or more in a solar application. 8000/365=22 years....and that assumes a full cycle every day!!

I believe SOK and EG4 use these cells. I am not sure who else uses them.

Jeff Goldblum is very excited by this news...

 

[fafrd]

To add to this, center charging/discharging lifepso4 batteries, just as you would with solar will make them last longer. We center tested some cells at work. They were cycled at ~25-75 soc. They just refused to die, we got >12k cycles at a way more aggressive profile than most people would use. We ended the testing before the cells failed. The full up and down cells crapped out months earlier.

For the sake of completeness, are you saying that the cells continued to deliver 75% of original 100% to 0% capacity when they were new or or that the cells continued to deliver 50% of original 100% to 0% capacity when new (75-25%) or that the cells suffered to loss of capacity versus the 100% to 0% capacity they had when new after 12k 25-75% cycles?

 

[zcskywire2]

For the sake of completeness, are you saying that the cells continued to deliver 75% of original 100% to 0% capacity when they were new or or that the cells continued to deliver 50% of original 100% to 0% capacity when new (75-25%) or that the cells suffered to loss of capacity versus the 100% to 0% capacity they had when new after 12k 25-75% cycles?

Twelve thousand 25% Soc to 75% soc cycles and back down cycles. They cells themselves still had ~80% original capacity afterwards and they had basically stopped declining in capacity.

 

[EastTexCowboy]

Depth of cycle matters. my first wife would wear me down to 0% almost daily. In 20 years I aged 40 years. Just the opposite with my forever wife. We've been together a little over 20 years and she recharges me way more than discharge every day. I now have a longer lifespan than I started with. Also I think there was a faulty bond on that first one ...

 

[sunsurfer]

Is there an efficiency loss as the cells get into the 80% range? I do like the 98% in and out.

 

[robby]

Two things will probably determine the fate of my batteries. The first is the question of what will be available in 10+ years and the second is will all the cells hold up or will one or two start having issues.

If they have a single packs on the market that are reasonably priced and can deliver the power of four packs of the same size made today then odds are I will be looking for any reason I can find to upgrade.

 

[scubadoo]

My 4 cell Sinopoly 300Ah battery has delivered about 5000kWh over the last nine years and counting with a 5% or so capacity loss. 315 down to 301Ah last November.
Number of cycles? Absolutely no idea!
I anticipate a few more years of usable life.

 

[wattmatters]

Number of cycles? Absolutely no idea!

Based on a typical BMS counting method, about 1630 cycles.

 

[robby]

I can verify that Fortress Power uses BMS‘s that count cycles as 100% down to 0%.
I cannot find a cycle counter in the one EG4-LL that is in my battery bank. I have never updated the firmware so I do not know if they added one in a later update.

 

[wattmatters]

I can verify that Fortress Power uses BMS‘s that count cycles as 100% down to 0%.

What if it never reaches 0%?

 

[Brett V]

You also have to account for calendar aging. The fact that LiFePO4 cell vendors sell at a discount after cells have been stored in the warehouse for a full year tells you everything you need to know about how significant calendar aging can be even if cells are not being cycled at all...

I'm not dismissing calendar aging but what you're actually seeing here is the cost of keeping inventory. No different than buying a 2022 Chevrolet at a discount after the 2023 models are out. Drop the price and get it gone.

 

[rhino]

I'm not dismissing calendar aging but what you're actually seeing here is the cost of keeping inventory. No different than buying a 2022 Chevrolet at a discount after the 2023 models are out. Drop the price and get it gone.

I don't think that is a good analogy since there is nothing wrong with the 2022 car and is still as good as new whereas the older LiFePO4 cell has actually degraded and is not like new.

 

[Robbert]

Would I be correct to assume that average ambient temps play a role in calendar aging?

There are some papers outlining that high ambient temperatures could lead to faster degradation.
That's the reason why I installed a mini split. Also good for the rest of the equipment in warm climates.