Charging to 70%, 80% or 90%

[budosteve]

All,

I acquired an inventory 100D in November and have been experimenting with charging levels. My results so far are not conclusive, so I propose the following question:

Assume I drive the same distance and utilize about the same amount of battery daily; maybe 20%

Environmental factors notwithstanding, will the energy consumed during charging change based on level which I choose to charge the battery?

Scenario 1: leave home w 90%, come home with 70%, charge back to 90%
Scenario 2: leave home w 80%, come home w 60%, charge to 80%
Scenario 3: leave home w 70%, come back w 50%, charge to 70%

Are each of these scenarios resulting in the same energy consumption during charging? The disconnnect I’m experiencing is related to the time it ostensibly takes to get from 80% to 90% being longer than from 50% to 60%, considering the kw consumption doesn’t change.

Looking forward to responses!

 

[ABC2D]

The disconnnect I’m experiencing is related to the time it ostensibly takes to get from 80% to 90% being longer than from 50% to 60%

If you have a supercharger (or CHAdeMO) at home then you may notice this, not with residential infrastructure.

 

[TMeister]

Any of your scenarios will take 40A/240V (most likely residential setup) for the whole charge with likely not measurable efficiency differences. Have you tried each of them under same conditions except SOC? I'd be surprised if they vary more than 5 minutes for the charge session. The issue for you is to keep the pack in the sweet spot for longevity. For that you would choose 70% to 50% and back to 70% for your daily use. Many articles to be found here on that subject.

 

[Graffi]

My normal charge limit is 70%. As long as you keep it around the 50% level you are good. At 70% I may discharge down to 60% or even 40% if I have extra driving.

Something I was told years ago, "Batteries do not die, they are murdered".

Try to avoid keeping a very high charge (unless you need it such as the start of a long drive), and a very low charge. I believe that discharging close to the bottom will cause more damage than charging to the top, but if possible, avoid both extremes. jmho

 

[TexasEV]

You’re all overthinking this. There many be measurable differences in battery life based on different charging scenarios, but they’re too small to be noticeable (statistically significant but not clinically meaningful, for those medical types among us who will understand the analogy). Practical experience with the Model S over the past 5 years shows routine charging to 90% does not result in significant battery degradation. For example, I’ve lost 5% range since July 2013, and there are plenty of other examples of this. It’s no different for people who haven’t charged that much. Anyway, if a 1 or 2 mile difference in range years later matters to you, you probably bought the wrong car.

 

[jdw]

I have about the same usage; what I do is charge to 90% timed to complete just before I leave. The car spends maybe 15 minutes at 90%, then I drive down to about 78-80% where the car stays at for 8 hours while at work and then drive home where the car sits at 65-70% for 12+ hours.

I find this keeps the average charge at a lower level, while still charging to 90%, which helps keep the battery calibration/balancing in line.

After 2.5 years and 22000 miles, I'm at 101% of delivery battery capacity.

 

[tnt1971]

I have read these threads, probably more than I should have. I too like to maximize my battery life. There are a lot of opinions out there about SOCs, depth of discharge, daily charge levels, etc. The only one I put a lot of faith in is the battery guru Tesla hired. I think his name is Jefferey Dahl or something like that. Anyway, after a ton of research of this brainiac, the conclusion was very simple: lower SOCs and lower temperatures are better. You can debate how much but based on his research and your driving habits, I would charge to 50% and drive down to 30% unless you need more. As others have written, the difference may be small, but if your goal is to maximize life and minimize degradation, that is the strategy I would follow.

Also, the out of balance and calibration, I believe, was resolved at some point. I have one of the last 85Ds produced, and I have never had a situation where a lower percentage of charge showed a different amount of miles than its higher percentage equivalent. Only low temperatures seems to change the RMs for a particular charge level.

 

[budosteve]

Thanks for all the responses! I’m not really concerned with longevity / lifetime range degradation as the effects are minimal in the real world.

My initial question still eludes... do I use a different amount of electricity charging from 40 to 60 than I do if I charge 70 to 90?

Simple fools math says yes...

It takes longer to charge from 70 to 90, all while consuming 7kw (I’m set at 30a and average 235v).

Or no?

 

[TexasEV]

No, at home charging rates it doesn’t take any longer to charge a given percentage until you're way over 90%. The earlier taper just applies to supercharging.

 

[Snowstorm]

Even when the taper happens you are not using more energy, just time. The power and current flow slows down at the top. As the previous poster said, the taper is only there at say 60-70% on a super charger. On a home level 2 charger, taper may happen closer to 98-99%.

 

[Buster1]

I use about 40% on my weekday commute. So I usually charge to 80 or 90% and arrive back home with 40 or 50%. On weekends I barely drive so I charge to 60 or 70%.

But I don’t know why. I just feel that this is better for the battery. Admittedly, I need to do some research on battery health/longevity.

 

[BerTX]

Even when the taper happens you are not using more energy, just time. The power and current flow slows down at the top. As the previous poster said, the taper is only there at say 60-70% on a super charger. On a home level 2 charger, taper may happen closer to 98-99%.

I can't quote a reference, but I remember someone concluding that the car has an overhead amount of energy it uses while charging (400W, I think?) regardless of the charge rate, so a longer amount of time would use slightly more power.

 

[Soolim]

Charge to 90% every other day. Two days driving takes it down to 50%.

 

[Snowstorm]

You are probably right that there is an overhead, but I do hope that it is less than 400w

I can't quote a reference, but I remember someone concluding that the car has an overhead amount of energy it uses while charging (400W, I think?) regardless of the charge rate, so a longer amount of time would use slightly more power.

 

[Peter Lucas]

You’re all overthinking this. There many be measurable differences in battery life based on different charging scenarios, but they’re too small to be noticeable (statistically significant but not clinically meaningful, for those medical types among us who will understand the analogy). Practical experience with the Model S over the past 5 years shows routine charging to 90% does not result in significant battery degradation. For example, I’ve lost 5% range since July 2013, and there are plenty of other examples of this. It’s no different for people who haven’t charged that much. Anyway, if a 1 or 2 mile difference in range years later matters to you, you probably bought the wrong car.

You claim that you have lost only 5% of range. How do you know? The cars calculation of range may be total fiction. It surely is on my car. Even after correcting for variations of wh/mile.
I have found that the state of charge indicator correlates very linearly with kwh consumed between 100% and 10% SOC. But the displayed miles of range remaining can only be achieved if my wh/mile is extremely low. Below the specified 324 wh/mile.

 

[Peter Lucas]

I have about the same usage; what I do is charge to 90% timed to complete just before I leave. The car spends maybe 15 minutes at 90%, then I drive down to about 78-80% where the car stays at for 8 hours while at work and then drive home where the car sits at 65-70% for 12+ hours.

I find this keeps the average charge at a lower level, while still charging to 90%, which helps keep the battery calibration/balancing in line.

After 2.5 years and 22000 miles, I'm at 101% of delivery battery capacity.

Just curious: how are you measuring your battery capacity?

 

[hacer]

You claim that you have lost only 5% of range. How do you know? The cars calculation of range may be total fiction. It surely is on my car. Even after correcting for variations of wh/mile.
I have found that the state of charge indicator correlates very linearly with kwh consumed between 100% and 10% SOC. But the displayed miles of range remaining can only be achieved if my wh/mile is extremely low. Below the specified 324 wh/mile.

It looks like you are using the EPA number for the "specified" wh/mile. That figure include the loss during charging; the energy display on the dash only includes the delivered power from the battery (so also excluding internal losses in the battery) and ignores vampire drain. So the wh/mile consumed from the battery is supposed to be quite a bit lower than the EPA number in order to get EPA range. In my car, in nice weather at highway speeds with fairly level terrain and no wind and a long stretch of driving, it is easily achievable. That's perfectly consistent with the way EPA ratings are defined.

 

[jdw]

Just curious: how are you measuring your battery capacity?

Visible Tesla & Remote S - comparing rated range at 90% and 100%, when new vs daily readings over the last 2.5 years. 239 miles@90% when new, 242 @ 90% now.

 

[TMeister]

...

My initial question still eludes... do I use a different amount of electricity charging from 40 to 60 than I do if I charge 70 to 90?

Simple fools math says yes...

It takes longer to charge from 70 to 90, all while consuming 7kw (I’m set at 30a and average 235v).

Or no?

All you have to do is run the experiment yourself. What's keeping you from doing that?

 

[Speedr117]

I too have a 100D. For me, it's more a balance between longevity and performance. I've read numerous places that 80% is the max you should charge if you don't need the range. But I also know (and has been proven by @Krash), that performance is diminished when you have less than 80% charge (at least on the 100D). So I end up charging to 83% every night. That way, I get the first few miles of full performance (wake up mode) before it tapers off.

Now I keep saying to myself, why didn't I just lease and not worry about this stuff...