Maximum charge level for daily use

[jcanoe]

I charge to 80% but find I only plug in my Model Y to charge two times per week. I usually wait until the state of charge (SOC) is down to ~50%. I know that if I need to charge from 80% to 90% that will only take about 1 hour (charging at home at 230V and 32 amps.) Charging from 80% to 100% would take something over 2 hours.

It's a car, there is no way to prevent someone from t-boning your baby or from a crazed forest creature darting out from the side of the road and smashing into your baby. I would not worry about whether to charge to 80% or up to 90%; these things are within your control. Now about that large space rock hurtling through space towards our planet, that I worry about.

 

[Arctic_White]

The manual does not say to use 90%. The car shows a range on the charge limit slider from 50% to 90% that is marked DAILY, and you get to pick where within that area works well for your balance of being nearer the middle if you want to be healthier for the battery, but being high enough that you have enough driving range to use.

That wouldn't make any sense at all, since 91% to 100% is not recommended for constant daily use and will display a warning if you do that. So 90% cannot magically be perfect if 91% is considered not recommended.

While I agree with you, I also know that there is no meaningful way to determine how BAD the battery degradation is (would be?) if we charge at 80% vs. 90%.

No one knows.

Do you definitively know?

 

[frankvb]

While I agree with you, I also know that there is no meaningful way to determine how BAD the battery degradation is (would be?) if we charge at 80% vs. 90%.

No one knows.

Do you definitively know?

The only thing we know with absolute certainty is that always charging it to 80% will not be worse than always charging it to 90%. But really it is common knowledge with these types of rechargeable batteries that it is better to keep the state of charge within 20 and 80%.

Then the question really becomes, is there a specific need to charge it to 90%? If not, most sensible would be to charge it to 80%. Why take the risk?

 

[jcanoe]

The battery pack will perform as designed over a finite number of charging cycles, let's say 3000 cycles (this is just an example.) This is for full charge and discharge cycles. For partial charging, say 40% to 80% charging, the battery will perform as designed over many more cycles, i.e. 2x or 3x as many cycles. With partial charging the battery pack could easily last beyond 10 or even 15 years although in all probability some other component will fail within that time. The mechanical links in the charging process, i.e. the charging station, charging connector and the charging port can and do wear out. By charging every other day, instead of every day that you don't need to charge it is logical that these components will last longer, i.e. twice as long, as if you charged every day.

 

[dhrivnak]

I'm not going to mark a disagree, because yes, a lot of Tesla sales people do tell customers 90%, but keep in mind that is a marketing number. They want to train their people to just have one number they can tell to everyone without having to have endless debates over the merits of higher or lower percentages for each person's unique driving habits.

Notice that the car has 50% to 90% marked as "Daily", and then 90% and above marked as "Trips", and the car will warn you if you use that 91% or higher for a few days in a row that it's not healthy for the battery. So think about that for a second. Since they recommend against using 91% or higher constantly, clearly 90% is not perfectly ideal. It doesn't magically go from being perfect to bad in that space between 90 and 91%.

Remember there are two issues we are trying avoid. First is battery degradation and yes 50% is ideal. The second is BMS calibration and balancing. The balancing likely does not occur below 80%. Both will cause problems.

 

[Rocky_H]

Remember there are two issues we are trying avoid. First is battery degradation and yes 50% is ideal. The second is BMS calibration and balancing. The balancing likely does not occur below 80%. Both will cause problems.

"problems"? The so-called "problem" from the BMS issue is paranoia in humans, not damage to the battery.

 

[Pilot1226]

I don’t believe that other thread suggested that balancing didn’t occur below 80%, I believe it said something like if the car doesn’t sleep or is actively charging then it won’t.

So if you set your max charge to, say, 50 or 60% and let it be, it should calibrate as the switch should be open.

 

[dhrivnak]

"problems"? The so-called "problem" from the BMS issue is paranoia in humans, not damage to the battery.

To a degree. The battery is actually a bunch of "bricks" a collection of cells. Over time they WILL drift apart and your range is limited to the weakest brick. So I agree no damage, but you will get reduced range, often significantly reduced range.

 

[frankvb]

To a degree. The battery is actually a bunch of "bricks" a collection of cells. Over time they WILL drift apart and your range is limited to the weakest brick. So I agree no damage, but you will get reduced range, often significantly reduced range.

The one detailed explanation I've seen that the Tesla batteries have an unusual way to balance the cells,using resistors to do some kind of continuous balancing. Not sure what to believe here though. Common sense would be to occasionally charge the batteries to 100%, and then make sure you do this before a trip that takes them back to below 90% or so. That is definitely better to keep the BMS tracking the real degradation state.

 

[alexcue]

The one detailed explanation I've seen that the Tesla batteries have an unusual way to balance the cells,using resistors to do some kind of continuous balancing. Not sure what to believe here though. Common sense would be to occasionally charge the batteries to 100%, and then make sure you do this before a trip that takes them back to below 90% or so. That is definitely better to keep the BMS tracking the real degradation state.

When life becomes "normal" again, that is my plan. Pick say 85% for everyday charging, and when I want to go on a longer, say 250 mile round trip, Charge to 100% right before, if i do some more miles than i planned, hit a SuperCharger for 15 minutes or so and then make sure i get back with 15-20% or so. I think that will achieve the balancing I'd want.

That's my plan in my head anyway...

 

[wk057]

To the OP, pick a level that fits your own needs. If you need 90% (including a buffer to be comfortable), then choose that. If you've got a 5 mile commute and rarely drive longer distances, pick 50%.

Realistically there is accelerated degradation any time you charge above 55% or so. It's not linear at all. The amount of degradation difference between 50% and 80% is pretty negligible. The difference between 80% and 90% still pretty tolerable. Above 90% consistently is where is gets bad, and you shouldn't go above 90% unless you need to (and when you do, use it as soon as possible to bring the charge below 90%).

I personally just charge all of my Tesla vehicles to 90% all the time. I'm good with the balance of slightly more degradation than 50% charges vs the convenience of having a mostly-charged vehicle available at a moment's notice.

 

[dhrivnak]

The one detailed explanation I've seen that the Tesla batteries have an unusual way to balance the cells,using resistors to do some kind of continuous balancing. Not sure what to believe here though. Common sense would be to occasionally charge the batteries to 100%, and then make sure you do this before a trip that takes them back to below 90% or so. That is definitely better to keep the BMS tracking the real degradation state.

Yes you are correct but the voltage of lithium cells is quite flat between 20% and 80%. You normally need to be near the top or bottom to see the differences between cells.

 

[amnesty_that]

I charge to 90% daily because

1. No home charger live in apartment

2. free charging at work

3. free destination charger 5 min walk away

4. i park outside so sentry mode always on. Lose about 10% a day. So typically when I’m ready to drive I’m at about 78-80%. My commute is only 22 miles RT.

5. I’m leasing so i do not care about degradation

6. I drive a performance Y and don’t you lose power at lower SOC?

Reading through comments i can definitely get away with charging to say 70% or even less during work week and 90% before weekend, but as the cost is zero to me, why would i not take 90% charge daily.

 

[jcanoe]

I charge to 90% daily because

1. No home charger live in apartment

2. free charging at work

3. free destination charger 5 min walk away

4. i park outside so sentry mode always on. Lose about 10% a day. So typically when I’m ready to drive I’m at about 78-80%. My commute is only 22 miles RT.

5. I’m leasing so i do not care about degradation

6. I drive a performance Y and don’t you lose power at lower SOC?

Reading through comments i can definitely get away with charging to say 70% or even less during work week and 90% before weekend, but as the cost is zero to me, why would i not take 90% charge daily.

Re #6, below 75% SOC the Tesla Model 3 Performance vehicle's two electric motors produced less HP. Instantaneous torque at 0 RPM was not nearly as impacted until the battery SOC dropped to below 40%.

More here: How Much Does State Of Charge Impact Tesla Model 3 Performance HP?

 

[HenryT]

The whole argument about 90% versus 70% (or some other number) seems to me to be an argument about something with virtually no 'real world' consequences anyway.

If, for example, routinely limiting charge to 70% means your battery's degradation is (say) 2% or 3% lower than it might have been if you had used a 90% daily figure, how will that 'extra' 2/3% benefit you? Other than a slightly higher visible anticipated mileage capacity at 100% SOC it is meaningless from a practical point of view, particularly if you don't charge to 100% anyway? Even then, Musk's view seems to be that 100% v 95% could be practically the same in mileage value, because of the benefit of regenerative braking being lost at 100%.

 

[MY-Y]

I find it interesting how quickly many will pull their areo caps off the Gemeni wheels and lose 7% of their range; the 7% range loss seems to be a non-issue when it comes to this cosmetic change.

If there there is a 7% range loss with battery degradation, it really bothers many owners. I actually understand the emotions behind battery degradation, but hoped the 7% aero cap loss non-issue would help provide some perspective.

 

[DanDi58]

I find it interesting how quickly many will pull their areo caps off the Gemeni wheels and lose 7% of their range; the 7% range loss seems to be a non-issue when it comes to this cosmetic change.

If there there is a 7% range loss with battery degradation, it really bothers many owners. I actually understand the emotions behind battery degradation, but hoped the 7% aero cap loss non-issue would help provide some perspective.

Is it really 7%? I've seen anecdotal info that suggests 1 - 2%. Where does the 7% number come from?

 

[Rocky_H]

If, for example, routinely limiting charge to 70% means your battery's degradation is (say) 2% or 3% lower than it might have been if you had used a 90% daily figure, how will that 'extra' 2/3% benefit you?

Are you willing to look at this through the other end of the telescope?

If you don't have need for all of that extra range every day, how would using a lower charge limit harm you?

This is a general principle that can be used with any kind of product. Why would you use something in a harsh way, shortening its life, if there isn't a need or a benefit to you from doing that? You could use the product more carefully and make it last longer by not abusing it without inconvenience. It's kind of the same type of reason you teach teenagers not to slam doors. There's no need to do it, and it's certainly not a good thing, even if you can't immediately point to what damage it's doing right at this moment.

 

[MY-Y]

Is it really 7%? I've seen anecdotal info that suggests 1 - 2%. Where does the 7% number come from?

I was surprised it was so high as well.

How Much Do Aerodynamic Tires Influence the Efficiency of the Tesla Model Y? - The Next Avenue

"On the outward journey with the covers, the car consumed 284 Wh per mile, and on the return 249 Wh per mile. Without the aerodynamic hubcaps, Model Y consumed 304 Wh per mile outbound and 278 Wh per mile on the way back. This represents a difference of 7.042% to the outbound and 7.631% to the return, remarkably high figures highlighting the importance of tires when optimizing aerodynamics."

 

[HenryT]

Are you willing to look at this through the other end of the telescope?

If you don't have need for all of that extra range every day, how would using a lower charge limit harm you?

This is a general principle that can be used with any kind of product. Why would you use something in a harsh way, shortening its life, if there isn't a need or a benefit to you from doing that? You could use the product more carefully and make it last longer by not abusing it without inconvenience. It's kind of the same type of reason you teach teenagers not to slam doors. There's no need to do it, and it's certainly not a good thing, even if you can't immediately point to what damage it's doing right at this moment.

I wouldn't have a problem at all, I just don't see it being that much of an issue either way in truth.

I have no expertise in the subject, but from what I have seen I'm not sure I would agree that (say) 90% v 80% as a baseline would be 'using it in a harsh way' or 'abusing it' as you put it.

My point was simply that I don't see how the 80% (or 70% if you like) user would be that much better off than a 90% user anyway. How exactly does the more conservative user benefit?