Battery Longevity Study

[slateya]

https://www.geotab.com/blog/ev-battery-health/

Busts some Myths.

Go ahead and use that 100% charge.

 

[Tom Sawyer]

Great article! Thanks for sharing.

Here's the Key Insights from the article:

• Average degradation rate: The average annual electric vehicle degradation rate is 2.3%.
• Power: High-power DC fast charging (>100kW) is the single largest stressor, leading to degradation rates up to twice that of the low power charging group (3.0% vs 1.5% per year).
• Climate: Hot climates impose a penalty on battery life, with vehicles operating in hot conditions degrading 0.4% faster per year than those in mild climates.
• Utilization: The increase in degradation from high daily use is a measurable but worthwhile trade-off for the gains in fleet productivity and ROI.
• State of charge (SOC): For most EV use, there's no need to worry about avoiding fully charging or emptying the battery. Degradation only speeds up when vehicles spend over 80% of their total time at or near-full or nearly empty charge levels.

If I understand the report correctly, extreme battery state of charge is okay, just don't stay there for extended periods.

 

[phidauex]

If I understand the report correctly, extreme battery state of charge is okay, just don't stay there for extended periods.

Exactly, for the stationary NMC batteries I work with, we track "hours over 90% SOC" as a metric. Being there overnight is a non-issue, but being there for 6 months straight would be noticeable.

 

[cadblu]

Interestingly, according to reliable sources Tesla is working on a new battery chemistry that will be optimized for a 90% charge for daily use (instead of 80%) as is recommended for NMC batteries. I think this is where the industry is headed.

 

[KevinRS]

Seeing similar numbers in other articles is part of why I think the standard battery will be fine for me, and for most people. The longest drive I'm likely to make will be about 137 miles, maybe a few times a year. That should be possible without charging on the way, by charging past 80% before making the trip. Even without that, it's like 5 minutes of charging somewhere mid trip. I wouldn't bother just charging for 5 minutes, I'd start the charge and get lunch, so probably 30 minutes.
That few times a year charging to 100% wouldn't really be detrimental, and would be useful to recalibrate anyway.
This is not on the other hand the right truck to make 300+ mile trips in, like LA to Vegas or similar. They would be possible, but a charging stop every couple of hours adds up. If someone needs to make that kind of trip often, they really shouldn't be looking at Slate as the vehicle to do it in.

 

[beatle]

Agreed on road trips. Though I've never feared degradation or charging to 100%, the EPA estimates for many vehicles are overstated when driving on the highway, even in good conditions. I have had some experiences in very cold and/or windy weather where I only got 60% of my rated range. Since that was in a car with ~335 miles of range, I still made it no problem with just one short charging stop, but with only 150 in ideal circumstances, I'd be stopping every 45 minutes and charging for just as long. I don't take long road trips, but it's not unusual for me to do 300 miles in a day trip hauling a motorcycle around.

 

[The Weatherman]

What I wonder is, is 90% the charge level of the entire battery or is it the usable portion where there is still % not seen or used by the BMS.?

For example: My Lightning has a 143 KWH battery. But, only 131 KWH is available to use. So when I charge to 90% on daily basis I’m only charging to 90% of the 131. That leaves 13KWH available for a buffer. Since there is already a buffer built in can I charge to 100% which would only be about 90% of the total battery?

 

[AZFox]

It comes down to whether you're a satisficer or a maximizer.

If your battery spends a lot of time charged to a high level it'll degrade more quickly, but that may be worth it to you for the convenience it provides.

OTOH you may prefer to keep the SOC in the middle range to preserve its capacity.

There's a lot of useful information in the first two videos in this post.

 

[Tom Sawyer]

What I wonder is, is 90% the charge level of the entire battery or is it the usable portion where there is still % not seen or used by the BMS.?

For example: My Lightning has a 143 KWH battery. But, only 131 KWH is available to use. So when I charge to 90% on daily basis I’m only charging to 90% of the 131. That leaves 13KWH available for a buffer. Since there is already a buffer built in can I charge to 100% which would only be about 90% of the total battery?

Is that 'buffer' unique to a Lightning?

 

[The Weatherman]

Is that 'buffer' unique to a Lightning?

No. It is present in all vehicles. There is an upper and lower buffer that the BMS does not consider when displaying state of charge (SOC).

It does vary from OEM to OEM though, so it’s hard to know how much is where (upper/lower).

 

[metroshot]

Is that 'buffer' unique to a Lightning?

Buffer exists in all EV and PHEV.

My Mustang Mach E has about 93% max charge limit due to the SOC top end buffer limit.

Thus, I always charge to 100% (93% actual) whether L2 or DCFC, knowing that the battery designers have already put in their math to last at least 8 years (HV warranty).