LiFePower4 Battery State of Health degradation...

[JLBinTN]

After roughly 350 charge-discharge cycles, my 5.12kw 48V LifePower4 battery's State of Health (SOH) dipped 0.3% to 99.7%. The Growatt SPF3000 All-in-one is set to cycle the battery between a 20% and 91% state of charge, but there have been one or two glitches where these parameters were exceeded. All that said, I'm wondering if a 0.3% decline in SOH over 350 cycles is reasonable, and what a chart of SOH vs Charge Cycles will look like over the estimated life of the battery (7000 cycles per the literature). Thoughts?

 

[SeaGal]

I wonder how the systems estimate SOH? Is it just number of cycles or based on some other measurable metric? If based on number of cycles and linear, then it's predicting 116,600+ cycles which sounds rather good to me!

 

[JLBinTN]

I wonder how the systems estimate SOH? Is it just number of cycles or based on some other measurable metric? If based on number of cycles and linear, then it's predicting 116,600+ cycles which sounds rather good to me!

That would indeed be pretty sweet! I'm guessing the degradation curve steepens significantly at some point however.

 

[Ampster]

That would indeed be pretty sweet! I'm guessing the degradation curve steepens significantly at some point however.

Possibly toward the end, below 50% for example.
Even though it is a different chemistry, my experience with EV batteries is that there is a steep initial degradation of 5-10% in the first year, then they plateau off for the next seven or eight. That is the longest I have owned an EV. I am still using some ten year old Nissan Leaf modules that still have 60-70% of capacity but I have no knowledge of their prior ownership,

 

[brucenolan]

I have 4 of the EG4 lifepower and here is my observation over the last year:


notice the different cycle count, two different purchases of 3 and 1 batteries. I am watching the 63 cycle battery drop 0.1 % every month. It was at 99.7 SOH when I put it in service. I would be happy to see 0.3 over 350 cycles.

Bruce

 

[JLBinTN]

I have 4 of the EG4 lifepower and here is my observation over the last year:

View attachment 130487
notice the different cycle count, two different purchases of 3 and 1 batteries. I am watching the 63 cycle battery drop 0.1 % every month. It was at 99.7 SOH when I put it in service. I would be happy to see 0.3 over 350 cycles.

Bruce

I'd be interested to see how this continues to change over time.

 

[Koldsimer]

I wonder how the systems estimate SOH? Is it just number of cycles or based on some other measurable metric? If based on number of cycles and linear, then it's predicting 116,600+ cycles which sounds rather good to me!

From what i have noticed it seems to be a combination of cycle counts and max amps pulled from the battery.

 

[brucenolan]

I'd be interested to see how this continues to change over time.

JLB,
I will keep this thread updated, I also have two more packs to be added when I get a rack set up. I will update SOH on all 6 at that time.

bruce

 

[JLBinTN]

JLB,
I will keep this thread updated, I also have two more packs to be added when I get a rack set up. I will update SOH on all 6 at that time.

bruce

Great!

 

[RCinFLA]

Pretty sure any SOH number it is creating is just based on discharge-charge cycle count. Very poor indicator.

A true SOH would require tracking of overpotential voltage (terminal voltage slump for given load current) degradation over time. This has to be done under fairly controlled conditions, most important being cell temperature must be known.

 

[sunshine_eggo]

First, I'm a pessimist. I doubt that this number has any meaningful predictive value. We've seen it vary dramatically with known cell balance issues.

Second, I'm far more inclined to believe this is the result of a balance issue. Given that you're not regularly charging to full and potentially not allowing sufficient balancing, the SoC accuracy may drift.

 

[timselectric]

I wouldn't put any stock in that imaginary value.

 

[brucenolan]

I'm not losing sleep over SOH from these, just makes me wonder why the difference? my packs get charged to balance voltage most every day (setting on SCC is 55.6 to absorb) that pack is usually less than 0.01 delta at full charge


edit: currently 0.027 delta during balance

 

[LithiumCowboy]

SOH is determined directly by capacity that's left. It determines the SOH and SOC by coulomb counting. You can recalibrate the SOH by fully cycling the battery multiple times. Following the 20%-80% rule for lifepo4 and the bms can become inaccurate by possibly one a few %. No battery BMS system is 100% accurate anyways as these are all estimations of the capacity that's left.

 

[LithiumCowboy]

Forgot to add, 0.3% for 350 cycles seems great. My 12v 400ah lifepower4 doesn't get enough use and wish I could cycle it more.

 

[shopman]

I have 4 of the EG4 lifepower and here is my observation over the last year:

View attachment 130487
notice the different cycle count, two different purchases of 3 and 1 batteries. I am watching the 63 cycle battery drop 0.1 % every month. It was at 99.7 SOH when I put it in service. I would be happy to see 0.3 over 350 cycles.

Bruce

When you fully charge the lower cycle count battery, does the loss in capacity show up as an overcharge percentage? I have two of them at 127 cycles where the capacity has fallen off to 98% when fully charged and the reported State of Charge is 102%. We're currently trying to figure out why. SS had me replace the BMS's in both batteries and they both went back to 100% capacity for about a week, but today I noticed the capacity/overcharge thing is returning. I'm wondering if the cells are defective or would you all consider this normal behavior for a babied set of batteries that are only 9 months old? I have two more of them that I purchased less than a month after the first two and they're both reporting 100% capacity after the same number of cycles. All batteries are hooked to the same system.

 

[brucenolan]

When you fully charge the lower cycle count battery, does the loss in capacity show up as an overcharge percentage? I have two of them at 127 cycles where the capacity has fallen off to 98% when fully charged and the reported State of Charge is 102%. We're currently trying to figure out why. SS had me replace the BMS's in both batteries and they both went back to 100% capacity for about a week, but today I noticed the capacity/overcharge thing is returning. I'm wondering if the cells are defective or would you all consider this normal behavior for a babied set of batteries that are only 9 months old? I have two more of them that I purchased less than a month after the first two and they're both reporting 100% capacity after the same number of cycles. All batteries are hooked to the same system.

I have not noticed SOC over 100%, I will observe today and see where it ends up

 

[brucenolan]

When you fully charge the lower cycle count battery, does the loss in capacity show up as an overcharge percentage? I have two of them at 127 cycles where the capacity has fallen off to 98% when fully charged and the reported State of Charge is 102%. We're currently trying to figure out why. SS had me replace the BMS's in both batteries and they both went back to 100% capacity for about a week, but today I noticed the capacity/overcharge thing is returning. I'm wondering if the cells are defective or would you all consider this normal behavior for a babied set of batteries that are only 9 months old? I have two more of them that I purchased less than a month after the first two and they're both reporting 100% capacity after the same number of cycles. All batteries are hooked to the same system.

Currently full and balancing, SOC on all 4 batteries at 100%

 

[brucenolan]

lost another 0.1 % less then 3 weeks between drop

 

[sunshine_eggo]

lost another 0.1 % less then 3 weeks between drop

View attachment 131001

If you're regularly charging to full as you indicate, I would anticipate that your SoH value may indeed be a result of perceived degradation; however, I wouldn't expect more than about ±5% of accuracy in terms of lifeprediction.

I'd be tempted to test it with a discharge to empty...