It's All About the Delta (and Temperature, but the BMS will Protect You) -- Test: Effect of temperature on battery cells life

[MADequipment]

Why don't you just summarize key results like any research paper would do instead of making us decode the graphs?

For example, in the charge graphs, some of the cells drop off a cliff at a low number of charge cycles. But is each test a single charge cycle or does it cover a group of charge cycles? Are some of your test batteries just bad?

The 45c graph shows a cell apparently dying after only 8 charge cycles. That seems extreme.

What do these results mean in the context of the BMS and its active cooling/heating?

Agreed. Should be laid out with the usual intro, methods, results, discussion. I appreciate the effort, but it’s impossible to read (and I didn’t skip to the graphs).

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[Grumpy2]

Agreed. Should be laid out with the usual intro, methods, results, discussion.

Seems like a real deal, except you will give up all benefits and be sued for exposing company owned products. Seems like something you would do? Just to benefit unnamed strangers that won't even read what has been posted.

Just wait a few years and perhaps those who paid $150k for the info will share with you.

 

[mr.Magoo]

The delta is centered on 50% SOC.

Very interesting stuff, thanks for sharing!

Did you guys do any "reference" tests with a higher or lower center point?

Ie, is it worse to go from 20 to 50 compared to 35 to 65, compared to 60 to 90 or is it more the extended charge cycles that's the bad guy when dealing with bigger delta?

You also mention that these are normalized, but can you tell what the charge currents used would equate to on a full pack / the truck ?

 

[lightspeed]

Seems like a real deal, except you will give up all benefits and be sued for exposing company owned products. Seems like something you would do? Just to benefit unnamed strangers that won't even read what has been posted.

Just wait a few years and perhaps those who paid $150k for the info will share with you.

Without full context, it would be hard to draw any realistic conclusions.

The calendar life tests don't make much sense. 45c/30%SOC didn't complete, 45c/50%SOC one cell apparently died after 8 weeks, 45c/80% seemed ok.

In the charge cycle tests, both cells died at 10/12 charge cycles at 25c/90%SOC. That seems extremely bad and implies that everyone's batteries will fail if they are charging to 90% which doesn't make much sense.

I have 26 RCTs worth of calendar aging and hundreds of charge cycles on my battery and it has only lost 1.5% of capacity. I

If you have a summary interpretation, why don't you share?

 

[admo]

This is some excellent data! If I am understanding the takeaways (and lack of mention of charge rate as important) it would seem charging amperage is not highly important to lifetime as long as the battery stays cool? So the suggestion that the 80amp charger should be turned down is not worth doing?

 

[lightspeed]

This is some excellent data! If I am understanding the takeaways (and lack of mention of charge rate as important) it would seem charging amperage is not highly important to lifetime as long as the battery stays cool? So the suggestion that the 80amp charger should be turned down is not worth doing?

Who knows. Can't say anything based on this data.

But 80amps is WAY below the 400-500amps that DC fast charging runs at. It's hard to imagine 80amps causing an issue.

 

[Alan168]

Thank you, MICKEYAO! I really appreciate all your efforts to educate us about our batteries.

I don't always understand everything I read the first time, but the info is there and as my knowledge base grows, I can return to it and understand more. I hope you continue to share your expertise because so many of us benefit from it.

 

[chl]

My basic takeaways are what I expected:

1) temperature is critical and too high a temperature is really bad for Li battery cells (so I will continue to avoid Fast DC charging, charging before letting the pack cool down, etc.);

2) battery life is also based on charge cycles (0% to 100% = 1 charge cycle; 40% to 90% - 1/2 cycle) but I would like to know: a) what the expected lifetime in charge cycles the Lightning pack have and b) how much difference the 'delta' really makes, neither of which I could glean from the data; and

3) better battery technology will come along in the next few years, probably before my Lightning has degraded much.

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