battery degradation: supercharge versus home charge

[David71201]

I recently purchased a used 2015 Model S 70 with 147K miles. Currently I am only able to charge at a supercharger ten minutes from my house in here in Monroe, LA. I realize that this degrades the batteries more than if I was charging at home. My question is, how much additional degradation should I expect?

A couple of notes:
1) I tend to go charge when it is around 50 miles and I charge to 180 miles. That has been about once every five days.
2) There are eight stalls; about 80% of the time I go there, I am the only one, and there has never been more than two others occupied (I would not want to be a supercharger hog).

Thanks.

 

[Babaron]

What’s the issue with not charging at home? Do you live in an apartment?

 

[David71201]

What’s the issue with not charging at home? Do you live in an apartment?

No, I have a house. The problem is that when I try to charge at home, the the charger blinks red twice, indicating no ground wire. But I do have a ground wire. So, until I can solve this mystery, I am unable to charge at home.

 

[Tam]

...how much additional degradation should I expect?...

Here's how a Tesla Model S holds up after 400,000 miles in 3 years - Electrek

Tesloop only supercharges with no home charge and it had to replace its battery 3 times in 400,000 miles.

The first time at 194,000 miles for a loss of 6%

The second at 324,000 miles with 22% loss.

I don't know what happened to the cause of the third battery replacement thanks to my reading comprehension

-----------

...charge when it is around 50 miles and I charge to 180 miles. That has been about once every five days....

You do know driving with a low state of charge is very stressful to your cells, don't you?

If you need to drive 180 - 50 = 130 miles, it's better to start at 90% or 216 miles on the battery gauge and ending with 86 miles and then charge it up.

Also, deeper discharge is not as good as a shallower discharge: It's better to recharge it every day rather than waiting for every 5 days.

 

[ucmndd]

You do know driving with a low state of charge is very stressful to your cells, don't you?

50 miles is north of 20% SoC on a S70. That’s far from “very stressful”. He also said in his first sentence he’s a new owner so the “you do know, don’t you?” condescension is not really warranted.

OP, what you’re doing now is fine and reasonable given your circumstances. Any additional degradation or stress on your battery is negligible over charging every day at home. Probably don’t do it forever, but you shouldn’t give it another thought in the short term.

 

[David71201]

Tam, the Tesloop data you provided is fascinating. I did click on the link and saw that they were charging to 100%. I am hoping that, by charging from about 20% to about 80%, my degradation will be lessened.

Incidentally, when I switch from miles to energy, it changes from (at the moment) 80 miles to 36%. That would imply that 100% would be about 222 miles. Do the miles (or energy) remaining take into account the fact that the batteries have 150K miles on them as well as driving and charging habits, or is it simply an unchanging straight line function (based on 222 miles at 100%)?

 

[AmpedRealtor]

You do know driving with a low state of charge is very stressful to your cells, don't you?

If you need to drive 180 - 50 = 130 miles, it's better to start at 90% or 216 miles on the battery gauge and ending with 86 miles and then charge it up.

Analysis and data from the #chargegate and #batterygate thread would seem to contradict your hypothesis. Charging a 85 kWh battery to 90% causes cooling pump to run for hours that does not happen at low SOC. This would indicate that holding a higher charge on these batteries causes stress not present at low SOC, otherwise why run the coolant pump?

Supercharging is also much faster if you stay in the bottom half of the battery instead of the top half.

 

[Tam]

...80 miles to 36%. That would imply that 100% would be about 222 miles. Do the miles (or energy) remaining take into account the fact that the batteries have 150K miles on them as well as driving and charging habits, or is it simply an unchanging straight line function (based on 222 miles at 100%)?

This is what I think:

When comparing numbers for degradation, you need to compare 100% to 100% at the same conditions such as room temperature.

It's not accurate to compare at 36% or 90% and extrapolate what 100% would be. It's a good academic, theoretic exercise though.

The battery gauge measurement is fixed: 100% = EPA number assigned, in your case, 216 miles, 0% = 0 mile.

My guess is when the voltage reduces at 100% full charge, the battery gauge would take that in as a factor and reduce the display range from the original 216 miles.

The calculation may drift with use which means it inaccurately display the wrong lower range.

To reduce that calculation drift, Tesla assumes owners would practice 90% charge at least daily.

You can charge anywhere from 50 to sub 90% daily but the calculation drifts can worsen although the actual range/battery capacity is more.

Let's say, your 100% = 216 miles but the battery gauge gradually drifts down to 100%=194.4 miles or a loss of 10%.

It's only a loss in display and not a loss in real range. That means you could drive pass 194.4 miles or 0% and the car still drives for another 21.6 miles and stall. But be cautioned that low state of charge is not good for your battery. 0% can permanently ruin your battery too.

 

[Tam]

Analysis and data from the #chargegate and #batterygate thread would seem to contradict your hypothesis. Charging a 85 kWh battery to 90% causes cooling pump to run for hours that does not happen at low SOC. This would indicate that holding a higher charge on these batteries causes stress not present at low SOC, otherwise why run the coolant pump?

Supercharging is also much faster if you stay in the bottom half of the battery instead of the top half.

A lower charge is about survivability and not about luxurious accessories.

Higher charge allows many accessories to work so that is a good thing.

As that battery is used, its voltage is reduced but the motor still needs to draw its same minimum energy requirement from the cell to move the car.

To compensate for that, the current pulling out of each cell is increased.

And that increased current flow demand is at the wrong time when the cell is weaker but the motor just doesn't care because it needs to move the car.

 

[sorka]

Just supercharge more frequently and keep it in as narrow range as possible. If you can keep it between 30 and 70% most of the time then supercharging won't result in any significant increase in degradation.

 

[brucet999]

No, I have a house. The problem is that when I try to charge at home, the the charger blinks red twice, indicating no ground wire. But I do have a ground wire. So, until I can solve this mystery, I am unable to charge at home.

Have you tested that ground wire, or do you simply know that a physical wire exists? It is a simple matter to use the two probes of a volt meter between hot of a 120V outlet and ground or between either of the hots of a 240V outlet and ground. If you do not see at least 115V, you do not have a connection to ground.

 

[VikH]

Just supercharge more frequently and keep it in as narrow range as possible. If you can keep it between 30 and 70% most of the time then supercharging won't result in any significant increase in degradation.

I think the better question is when will they hit DC limit for the 70 pack.

 

[dk10438]

I recently purchased a used 2015 Model S 70 with 147K miles. Currently I am only able to charge at a supercharger ten minutes from my house in here in Monroe, LA. I realize that this degrades the batteries more than if I was charging at home. My question is, how much additional degradation should I expect?

A couple of notes:
1) I tend to go charge when it is around 50 miles and I charge to 180 miles. That has been about once every five days.
2) There are eight stalls; about 80% of the time I go there, I am the only one, and there has never been more than two others occupied (I would not want to be a supercharger hog).

Thanks.

Personally I do not think it makes any difference. I pretty much home charged to 70% every day and at 20k miles I have 7.5% degradation. There's plenty of people that supercharge frequently and they have minimal degradation. Degradation seems to be more random than related to specific charging behaviors....

 

[brucet999]

Personally I do not think it makes any difference. I pretty much home charged to 70% every day and at 20k miles I have 7.5% degradation. There's plenty of people that supercharge frequently and they have minimal degradation. Degradation seems to be more random than related to specific charging behaviors....

Wow. That's pretty big degradation for 20k miles. I have 43k on my MS70 with 3.3% degradation.