Simple Question. Better to Charge to 80% or 90%

[M109Rider]

In Ontario, even in the north, I would not worry about -30C for 24 hours at a time. Yes, the nighttime low may hit -30, but I would be hard pressed to find any day in he past 30 year where I have understanding of what temperature it is when the entire day is below -30. If you are inside a garage, you are double fine.

I agree it isn’t common, but last year we had a string of I think a week or two in early January that I personally remember it going below -35 for lows.
I recall New Year’s Eve being particularly nasty.
It does happen enough these days, but off and on January to February.

 

[Kichwas]

Necroing an old thread rather than asking the question over again, to basically...
Ask the question over again.

The consensus in the thread seemed to be, no consensus and doesn’t matter.

But now that the car is in the hands of much more people, and has been through a few updates and folks have had it longer...

Is there any consensus yet?

90%, 80%, or what?

 

[Blu Angel]

@Kichwas,

Jeff Dahn, renowned battery researcher, currently working with Tesla Inc, ideally recommends a 70/30 split.
Daily charging to Max 70% and minimum charge down to 30%

Tesla battery expert recommends daily charging limit to optimize durability

 

[Shock-On-T]

Necroing an old thread rather than asking the question over again, to basically...
Ask the question over again.

The consensus in the thread seemed to be, no consensus and doesn’t matter.

But now that the car is in the hands of much more people, and has been through a few updates and folks have had it longer...

Is there any consensus yet?

90%, 80%, or what?

Simple rule: closer to 50% the better, but doesn't matter much.

 

[Shock-On-T]

@TexasEV why the disagree on above?

 

[wdolson]

The core answer is the exact target doesn't matter that much, just avoid going over 90% unless you are planning on driving the car immediately, and don't go below 10-20% if possible. For practicality your set point should probably be above 50%, but it really doesn't matter that much. Different people have chosen different charge levels within that range and the results for battery life are about the same.

 

[MaryAnning3]

This is a great thread. Thanks a lot everybody! (Jamnmon et al. ...) I learned a lot.

 

[MaryAnning3]

This was my question as well. I would expect garage to be somewhat higher temp.

It is inexpensive and easy to measure temperature and record max and min.

 

[MaryAnning3]

I think going low tends to be a bit worse than going high. As in, an excursion to 8% causes more diminishment than an excursion to 92%. Could anyone support or refute?

Thus I think, in a apocalyptic future where you have only one car forever (and solar panels), charging/discharging between 33% and 73% might be slightly preferable to 30% to 70% for everyday use. Anyone?

 

[David99]

I think going low tends to be a bit worse than going high. As in, an excursion to 8% causes more diminishment than an excursion to 92%. Could anyone support or refute?

Thus I think, in a apocalyptic future where you have only one car forever (and solar panels), charging/discharging between 33% and 73% might be slightly preferable to 30% to 70% for everyday use. Anyone?

I think the answer isn't simple. Lots of things play in. Discharging to a low level is fine if you do it slow. Driving hard when the battery is at 5% is definitey not good. That's why Tesla limits the power when the battery is low. Same when the battery is cold. So is 5% at normal temperature the same as 10% at freezing? And what power draw is how damaging at what battery level? It's just several factors all playing together. We can only guess. But in the end, Tesla has put a BMS in place that prevents you from damaging the battery. It monitors all factors (temperature, charge level, age, internal resistance, ...) and sets certain limits. You cannot exceed those limits. I have driven my car to all these limits a lot. 181k miles. Many times down to zero, many times charged to 100%, many times driven in extreme heat and supercharged over and over in all conditions. My degradation is not worse than other cars with similar miles. That gives me confidence that we don't have to worry too much. Going forward Tesla's batteries are only getting better.

 

[David99]

I think going low tends to be a bit worse than going high. As in, an excursion to 8% causes more diminishment than an excursion to 92%. Could anyone support or refute?

Thus I think, in a apocalyptic future where you have only one car forever (and solar panels), charging/discharging between 33% and 73% might be slightly preferable to 30% to 70% for everyday use. Anyone?

I don't think we need to worry too much about it. My battery went through a lot in 180k miles. I drove it down to 0% many times. I discharge below 10% a lot. I charge to 100% when I need it without hesitation. I supercharge a lot. Extreme heat and supercharging many times. My degradation isn't worse than other cars with similar mileage. Tesla's BMS sets limits based on all the factors that are important so it's impossible to damage the battery. Sure there are some things you can do to baby your battery, but comparing high mileage cars they show little difference in degradation. I think it's common sense to avoid extremes in every aspect (temperature, driving style, charge levels, ...) but other than that, just drive it.

The fact that Tesla reserves the bottom 8% but let's you charge to true 100% might indicate that lower is worse than higher. But then, since they already protect the lower end, we can safely use the entire range they are giving us.

 

[Kichwas]

The most recent video from “Like Tesla:

Goes into some battery things. I noticed she was charged to 100% but only showed 260 range...
She also talked about there possibly being as much as 100 miles available after you hit 0% depending on how you drive...

Not sure what I thought of her claims there, or her handwaving away of the 260 at 100% charge as a non-issue (if that was my car it would be getting a service appointment).

But it was interesting and relevant here nonetheless.

 

[Bill45]

I used to charge my car to 90%, then adjusted to 80% (my daily commute is similar to yours), but it should not really matter between the two. Both the phone app and the on-screen indicator in the car let you set the value for daily (50-90%) or trip (90-100%), so as long as you keep it within the daily threshold you will be fine.

I used to charge my car to 90%, then adjusted to 80% (my daily commute is similar to yours), but it should not really matter between the two. Both the phone app and the on-screen indicator in the car let you set the value for daily (50-90%) or trip (90-100%), so as long as you keep it within the daily threshold you will be fine.

I have heard that there is likely a 10% battery reserve; so if you charge to 90% the battery is only 80% charged. Does anyone know if that is correct?

 

[tomas]

It WAS a simple question, right? Wrong.

The answer is actually both are OK, don't worry, be happy!

 

[David99]

I have heard that there is likely a 10% battery reserve; so if you charge to 90% the battery is only 80% charged. Does anyone know if that is correct?

No 100% is truly 100% based on the voltage of the cells.

 

[TexasEV]

I have heard that there is likely a 10% battery reserve; so if you charge to 90% the battery is only 80% charged. Does anyone know if that is correct?

No it’s not correct.

 

[wdolson]

I have heard that there is likely a 10% battery reserve; so if you charge to 90% the battery is only 80% charged. Does anyone know if that is correct?

There has been speculation that there is an anti-bricking reserve on the low end to prevent the battery from actually discharging to 0, but I have also seen some experts say that isn't there. The software limited 60s appear to be chargeable to 100% without risk because 100% on one of those batteries is 80%, but the software limited batteries are the only ones where you can charge to 100% without concern. For the rest, 100% is 100%.

 

[Rocky_H]

There has been speculation that there is an anti-bricking reserve on the low end to prevent the battery from actually discharging to 0, but I have also seen some experts say that isn't there.

That is absolutely known to be there, but that is different than this 10% at the top end that @Sporky asked about.

 

[NickFie]

95% in the winter

When I’m on a road trip and charge above 90% several consecutive days, the charging panel warns me against the practice.