"Best practice EV charging for longer battery life" - video

[Tooney]

"This video is made with a specific audience in mind, EV owners who drive less than 25 miles or 40kms each day and charge at home. Statistics suggest that is the majority of commuters in developed countries. If it's not you then feel free to skip to the next video.
The testing data pertains to "ternary" chemistry (e.g. NMC, NCA) and not LFP.
Key takeaways:
1. Most EVs allow you to set the maximum state of charge (SOC). You don’t have to choose 90%
2. Testing conducted by independent labs shows that leaving lithium-ion batteries at a high SOC for prolonged periods can shorten their life
3. Li-ion batteries are least stressed when at 50% SOC, which is why most products are shipped at 50% SOC
4. If you only use 10% (or less) of your battery capacity each day then there is no need to top it up to 90% each night. Indeed this could be counter-productive since your battery will reach 90% after an hour or so and then stand fully charged for up to 12 hours in your garage.
5. If you only need 10% for your daily drive then I recommend you drop your maximum SOC to allow for this (maybe 60%). You can always increase it whenever you are planning to drive further in a day.
6. You don’t have to follow this advice. Your battery, your choice. But this is a no-regrets approach since worst case it will make no difference to your battery life and best case it will enhance it.
Data is sourced from The Battery University and Chalmers University of Technology."

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[enzo5000]

Great video. I watched it the other day. I'm changing my battery charging for daily use to 80% max and 40% min.

 

[DougFrisk]

I need to do some research on their methods, but I'm somewhat confused on what a cycle is in that graph. Is it equivalent full discharge cycle or are the cycles of varying depth? If it's the latter, then for a ten percent cycle you have to go out five times further in the graph than with a fifty percent cycle to get an equivalent total consumption and the graphs are misleading.

 

[Vim Schrotnock]

As @DougFrisk commented, the graph is quite confusing. This is a terrible analysis of data, and completely misses the most important point shown in what is really a very misleading graph. I am no expert in this area, but I can read a graph and interpret simple data. My understanding is that battery life is highly dependent upon the TOTAL charging energy transferred to the battery over its life. That is, how many kWh of energy have I transferred to the battery over its lifetime. At least for the data presented in the video, this is a terribly misleading graph, and the conclusion is not supported by the data shown.

If I charge from 25%-85%, this is charging the battery with 60% of its capacity each DST cycle. For simplicity, let's assume I have a battery with a capacity of 100kWh. This means each charging cycle I'm putting 60kWh of energy into the battery. After 1,000 charging cycles, I've cycled the battery through a total of 60,000 kWh of energy charging. If I charge the battery with a charging cycle of 65%-75%, I'm only charging 10% of the capacity each time, or 10kWh. To get the same total of kWh charging over the life of the battery, I would need to charge 6,000 cycles to get a total of 60,000 kWh energy transferred.

If you want to compare two batteries that have both experienced the same total charging energy over their lifetime, then compare the 25%-85% battery at 1,000 cycles to the 75%-65% battery at 6,000 cycles. Both batteries would have experienced the same 60,000kWh energy transfer over their lifetimes. As you can see from the graph, both batteries (the green line and the gold line) are at about 93% capacity. No difference.

 

[DougFrisk]

Some of them are directly comparable. The 100% to 40% and the 85% - 25% both cycle the battery 60% on each cycle and there is a significant difference bethwen them. Similarly the 100% to 50% and the 75% to 25% are directly comparable. It would be nice to see a 95%-85%, an 85%-75%, a 75%-65%, a 65% - 55%, and a 55%-45%.

 

[Scandinavian]

I need to do some research on their methods, but I'm somewhat confused on what a cycle is in that graph. Is it equivalent full discharge cycle or are the cycles of varying depth? If it's the latter, then for a ten percent cycle you have to go out five times further in the graph than with a fifty percent cycle to get an equivalent total consumption and the graphs are misleading.

They are defining a charge cycle as the charge from say 65% to 75%, ie only 0.1 of a cycle as known for EV’s. They call Dynamic Stress Test cycle.

The video is not much of value at all.

 

[Vim Schrotnock]

Some of them are directly comparable. The 100% to 40% and the 85% - 25% both cycle the battery 60% on each cycle and there is a significant difference bethwen them. Similarly the 100% to 50% and the 75% to 25% are directly comparable. It would be nice to see a 95%-85%, an 85%-75%, a 75%-65%, a 65% - 55%, and a 55%-45%.

Yes, this is another significant problem with the data as presented. Everyone will agree that charging frequently to 100% will degrade the battery, so again, this is not a good comparison. To your point, looking at frequent charging of 10% at various levels such as 85%-75% would be a much better comparison. Given the lack of basic good experimental design and data presentation here, I would discount pretty much anything coming from 'The Battery University', which does not have any kind of certification, industry relationships, or peer-reviewed publications in any major journals that I can identify.

 

[Scandinavian]

Here is a video with Dr Jeff Dahn. Probably one of the most knowledgable person of battery technology. It is a long video, but well worth watching.

 

[Vim Schrotnock]

Here is a video with Dr Jeff Dahn. Probabilistisk one of the most knowledgable person of battery technology. It is a long video, but well worth watching.

"Lots of short drives with frequent charging is better than charging infrequently" And he's recommending 75% charge with frequent, small charges as opposed to infrequent larger charges. I'll continue with my 85%, topping off every day.

Also interesting on the ambient temperature effect on the optimal SOC. Folks in AZ are at a definite disadvantage here...

 

[DougFrisk]

Here is a video with Dr Jeff Dahn. Probably one of the most knowledgable person of battery technology. It is a long video, but well worth watching.

That was fascinating. I was particularly interested in the bits about physical deformation of the electrodes during charge and discharge causing microcracking. The Taycan battery is NCM712 so probably close to the 811 chemistry in these graphs and he stated that the dips at the higher states of charge correspond to large physical changes in the electrodes.

Minimizing mechanical stress on the electrodes would be a matter of finding the points on the graphs below where the slope is minimized across both graphs. For the a axis that appears to be between 60% and 90% SOC and for the c axis it appears to be about 40% and 75%. Again, the Taycan uses 712 and these are 622 so not exact, but possibly a good proxy. So it seems you may be able to minimize mechanical stress and with it microcracking by aiming to charge to 75% on a daiiy basis. Which turns out to be the exact number he suggested.

The guessometer in our car would be at 180 miles of range at 75% and we already charge daily, plus with the 11.5KW charger we can perform an 85% charge in the 6 hour low cost electricity window so if we do need to fully charge for a trip it can still be done cheaply. If we had a 6KW charger I might be more concerned with keeping the battery above 60% at a minimum during daily use.

 

[Vercingetorix]

Why does any of this need to be presented in video form?

 

[FlyingPoint]

Typical Porsche owner - save it for the next person - not me. I charge to what is most convenient for me at the time and could care less. I have more than paid for the privilege and don't plan on keeping my Taycan more than the warranty will cover. I would have thought that this mantra would have died with the EV, but congrats Porsche, all is alive an well.

 

[DougFrisk]

Just a minor update. The video by Dr. Dahn stated that a cell voltage of 4.06 volts equated to 75% state of charge for that cell. I threw the scanner on the car just now and 76% as reported by the car equates to a cell voltage of 3.93 volts. If 4.2 is 100%, then the cell's 75% is probably between the car's 80% and 85%.

 

[Vim Schrotnock]

For some real-world data, I've been charging at home at 35-40 Amps for the three years and 33,000 mi I've had my Turbo S. Charging pretty much every day to 85%. Very rarely charged to 100% (maybe a dozen times), and only 20 or so 'fast charges' at Electrify America over that time.

I had two bad cells identified and both modules replaced a couple months ago. My battery SOH is 92.6% as measured by the specialized battery technician they flew in from Atlanta - so I believe this is a good number. If you take out the 2/33 modules that are effectively 100%, that gives 92.1% SOH of the other cells. I think this supports the method of daily at-home charging to 85%.

 

[nischalr]

Technology is changing too fast, new battery tech and new car before this car wears itself out I would think even under a worst case?

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