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How to take care of your battery without stressing: advice for new owners.

PhysicsGuy

Member
Apr 16, 2020
100
89
California
I have gotten a great deal of benefit from this forum, but I have become concerned that people are getting unsound advice here about how to take care of your battery. Specifically, there are recommendations of things you can do to increase your range that I think are not actually good for your battery.

Taking care of your battery[1,2] is simple and does not require a Ph.D.. I keep my battery between about 30% and 70% for everyday use and then charge to about 95% before I go on a longer trip. You can charge your battery to 90% everyday if you prefer to do that. It is no big deal. I would recommend avoiding going below 15% or 12% unless you are really in a pinch. That is pretty much it. Charging speed is not too important; Tesla knows what they are doing at superchargers. There is one other small thing. Acceleration comes at a small cost. Accelerate all you want, but realize the it diminishes the longevity of your battery very slightly because you are drawing current from your battery at a very high rate[3].

Things that concern me here include recommendations that people charge to 95% and drain to 5% three times for the purpose of increasing your range. This can make the range you see on your display higher, which is ironic because doing those three cycles definitely decreases the capacity of your battery in kW-h (kilo Watt hours). This is just the way the chemistry and physics of the cells in your battery work. There is no way around it. Your battery has a finite number of cycles. It is a large number, but it is finite. You have just wasted 3 of them for the momentary pleasure of seeing a higher number on your screen. This may be called “touching the shore”, which is not only bad for your cells, but has a theory behind it that is unsound because there is a simple relationship between state of charge and voltage that does not change as cells age. The thing that changes is the number of kW-h of energy that your battery stores.

Additionally, going to a high or low state of charge for the purpose of balancing is, for the most part, unnecessary. Tesla is able to monitor the degree of imbalance among your 96 groups of cells. I think they would let you know if that becomes problematic. They monitor intermediate voltages between groups that we cannot see. If your groups are slightly out of balance, the worst thing you can do is go below 12%, because that exposes your weakest groups to bullying by the stronger groups (I.e., getting current pushed through them that they can’t handle well).

It is pretty simple. Charge above 90% only just before you go on a trip. Endeavor to never go below 12%. Sustained acceleration is not free.

Oh, and here is the most important thing that I almost forgot. Set your range to percent, not to miles or kilometers. That will create a good mindset for paying attention to your batteries very simple needs and avoid range obsession. If you need to know how far you can drive, assume 10% will give you at least 25 miles[4].

————

1. Your battery is made of cells. It starts with groups of 46 cells in parallel; which establishes a high current capacity. Your battery, in a model 3, is a string of 96 of these groups. It has a high voltage, basically 96 times 3.7 volts at 50% charge and no load. (Be careful who you take advice from. Tesla techs are not generally Li-ion battery experts.

2. There is a relationship between voltage and percent charge at the cellular level, and therefore at all levels. For example:
4.11 volts is 92%
3.97 volts is 80%
3.69 volts is 50%
3.50 volts is 20%
3.4 volts is 12%
Going below 12% is bad for your cells.

3. For normal highway driving your battery would drain to zero in about 3 hours. That means it is drawing current at a rate called C/3. When you accelerate, Tesla allows you to draw about 5C. That is a high rate of current draw, but it is not a big deal because it is for a very brief time. In general, drawing current from a Li-ion battery at more than 2C tends to reduce the battery's longevity.

4. Range table.
10%. 25 miles
20% 50 miles
30% 75 miles
40% 100 miles

80% 200 miles

Or, more optimistically:
10%. 30 miles
20% 60 miles
30% 90 miles
40% 120 miles

80% 240 miles
The truth will probably lie somewhere in between depending on local conditions, including wind. I get noticeably more range going south than north on 101.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,660
7,954
Boise, ID
Ooohh, and you were doing so well...

I agree with all of this about the charging levels, except for telling people to set the display for % and doing that in bold font. That's your preference you are projecting on people. I do agree that some people really can't handle seeing "rated miles". I've seen plenty of people foaming at the mouth, losing their everlovin' minds because the rated miles don't always equate 1 to 1 with real distance miles driven, and they absolutely just can't handle that without throwing a fit. It's like an OCD thing or something because they see that as "wrong". So yes, they need to switch to % to just not see that or think about that so they can stay calm. But humans don't think about real distances of places they go in percentages. People who are more laid back and not bothered with it can be comfortable just knowing that "rated miles" are always ballpark higher than real miles, and 84 miles of real driving today needs probably 120ish rated to comfortably do that.

But that is reopening what should have been an unrelated and overly debated can of worms. Thank you for the recommendations about charging levels.
 

PhysicsGuy

Member
Apr 16, 2020
100
89
California
Ooohh, and you were doing so well...

I agree with all of this about the charging levels, except for telling people to set the display for % and doing that in bold font. That's your preference you are projecting on people. I do agree that some people really can't handle seeing "rated miles". I've seen plenty of people foaming at the mouth, losing their everlovin' minds because the rated miles don't always equate 1 to 1 with real distance miles driven, and they absolutely just can't handle that without throwing a fit. It's like an OCD thing or something because they see that as "wrong". So yes, they need to switch to % to just not see that or think about that so they can stay calm. But humans don't think about real distances of places they go in percentages. People who are more laid back and not bothered with it can be comfortable just knowing that "rated miles" are always ballpark higher than real miles, and 84 miles of real driving today needs probably 120ish rated to comfortably do that.

But that is reopening what should have been an unrelated and overly debated can of worms. Thank you for the recommendations about charging levels.
Aaaarrrg. Sorry about the bold font there. My bad. You are totally right.
 
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dmurphy

Buster: 11/25/14 - 6/20/21. So sorely missed.
Supporting Member
Dec 7, 2018
3,786
5,135
New Jersey - Morris County
I agree with all of this about the charging levels, except for telling people to set the display for % and doing that in bold font. That's your preference you are projecting on people. ....

People who are more laid back and not bothered with it can be comfortable just knowing that "rated miles" are always ballpark higher than real miles, and 84 miles of real driving today needs probably 120ish rated to comfortably do that.

ROWRY!


When driving a gas vehicle, I stopped paying attention to gas gauges decades ago. Ever since the "XX miles to empty" estimator came along; I'm much happier using that as an estimate of range.

I feel much the same about the Tesla mileage gauge. Road signs are measured in miles, not percentages. Knowing there's 24% battery remaining doesn't give me any clue as to whether I'll make it to my destination or not. Having a mileage display - with a fudge factor - does.

And, to quote yet another great movie .... "That's all I have to say about that."
 

camalaio

Active Member
May 28, 2019
1,483
2,106
Vernon, BC, Canada
Aaaarrrg. Sorry about the bold font there. My bad. You are totally right.

Haha, thanks for taking it well! I had the exact same reaction as @Rocky_H :D
In the situation where the battery is degraded, Person A's mi/% may be very different from Person B's mi/%. But far more importantly, the mi/% varies between Long Range vs. SR+ quite a bit! For discussion between vehicles on this forum, rated miles consumption is much more handy because it's equivalent to a unit of energy, whereas percent without knowing which battery size is not. This also means that climate control actually takes more percent of the battery on an SR+. It's part of why those little EV work vehicles with "100km range" or so can barely go anywhere once you turn the heater on.

If I may nitpick a couple things for correctness though, since there's some technical details:
  • I'm not sure where your voltages come from, but mine are a bit different (mostly higher, even though not open-circuit). Are these generalised numbers for similar Li-ion cells? It seems like they might be, which doesn't quite match the displayed percentage for the Model 3. My numbers follow, close to 25C/77F:
    • ~4.15V @ 95%
    • ~4.12V @ 93%
    • ~4.08V @ 80%
    • ~4.00V @ ~72%
    • ~3.89V @ 60%
    • ~3.80V @ 50%
    • Any data I have for lower numbers is highly confounded (hot battery, too much power draw, etc.)
  • It's not always 46 parallel cells. See: Long Range vs. Mid Range vs. SR
  • Percent-to-miles doesn't work since battery size varies (see above).
I think an important-but-not-emphasised point in your post is this: "Tesla techs are not generally Li-ion battery experts". This is so, so incredibly unfortunate for the owners, especially when they hand-wave or blame the owner for bad charging practices that are actually good (sometimes even recommended by a different tech). We get mixed signals from different Tesla employees, Elon, folks on this forum, actual battery people, etc. At the end of the day (though people hate the comparison for some very valid reasons), you can often compare your phone battery to your car battery quite successfully since Tesla isn't that different in that regard. The differences bring up good discussion points.
 

SeaNile

Member
May 27, 2019
92
62
Chadds Ford, PA
And I was getting to very close to buying a Y until i read the one sentence on here. Range is about 3hrs of highway driving......that doesn't sit well with me. I am in my car for hours a day with a varying commute, rarely going to the same place in the same order (sales). So if I am to get in my Y in Philadelphia and need to get to Lewes, DE, there may not be enough range to make it without stopping. I can make this drive easily now in my ICE car and can get to Lewes AND back on one tank with plenty to spare.

I am so on the fence about Tesla. Some days I feel like I am over thinking everything and other days my gut tells me something must be a serious concern of mine otherwise I would have bought a M3 years ago. This coming from someone who has owned 48 (or it is 49, 50) vehicles.
 
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dmurphy

Buster: 11/25/14 - 6/20/21. So sorely missed.
Supporting Member
Dec 7, 2018
3,786
5,135
New Jersey - Morris County
And I was getting to very close to buying a Y until i read the one sentence on here. Range is about 3hrs of highway driving......that doesn't sit well with me. I am in my car for hours a day with a varying commute, rarely going to the same place in the same order (sales). So if I am to get in my Y in Philadelphia and need to get to Lewes, DE, there may not be enough range to make it without stopping. I can make this drive easily now in my ICE car and can get to Lewes AND back on one tank with plenty to spare.

I am so on the fence about Tesla. Some days I feel like I am over thinking everything and other days my gut tells me something must be a serious concern of mine otherwise I would have bought a M3 years ago. This coming from someone who has owned 48 (or it is 49, 50) vehicles.

You *are* overthinking it, I assure you. :)

I've had no problem driving my Model 3 LR AWD from Morristown NJ to Lewes DE, including picking someone up in Secaucus. I did need to charge in Lewes before coming home, but the Supercharger there is awesome - right at the Wawa. (And in fact, my rented condo in Lewes was right next door on Summerlyn Dr.)

Keep in mind, the LR AWD Model Y has a higher rated range than my 3, so you'd be even better off.

You'll be fine. And even if you're beyond range once in a blue moon, a 10 minute Supercharger stop would work. I did one a few weeks ago at one of the "Version 3" Superchargers. Got about 150 miles of range in 10 minutes. Enough time to stop, take a leak, grab a bottle of water at the Wawa, get back to the car, and keep going.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,660
7,954
Boise, ID
And I was getting to very close to buying a Y until i read the one sentence on here. Range is about 3hrs of highway driving......that doesn't sit well with me. I am in my car for hours a day with a varying commute, rarely going to the same place in the same order (sales). So if I am to get in my Y in Philadelphia and need to get to Lewes, DE, there may not be enough range to make it without stopping. I can make this drive easily now in my ICE car and can get to Lewes AND back on one tank with plenty to spare.

I am so on the fence about Tesla. Some days I feel like I am over thinking everything and other days my gut tells me something must be a serious concern of mine otherwise I would have bought a M3 years ago. This coming from someone who has owned 48 (or it is 49, 50) vehicles.
We see it frequently, but you have a very ingrained set of gas car mindsets and assumptions and habits built up, and are just perceiving negatively anything that might be different. I sometimes don't get this insistence by gas car drivers that any trip that needs to be made must be done without any stops. Why?

I appreciate your giving an example, so we can talk about it. Philadelpha to Lewes is about 120 miles, taking I-95. You pass right through Wilmington and Dover, and both have Superchargers. You wouldn't need to stop in both directions, but only one stop--either on the way there or the way back--would make this easy. With a four hour round trip, you can't fit in a 15-20 minute break on either side?

That's just the adjustment of assumptions and midset that make this easy if you can adapt to that. Instead of insisting on always being able to do 4-5+ hours non-stop, how about some willingness to take shorter segments with a couple of breaks here and there to use the bathroom, get a coffee, and then get back on the road? It's not bad.
 

SeaNile

Member
May 27, 2019
92
62
Chadds Ford, PA
We see it frequently, but you have a very ingrained set of gas car mindsets and assumptions and habits built up, and are just perceiving negatively anything that might be different. I sometimes don't get this insistence by gas car drivers that any trip that needs to be made must be done without any stops. Why?

I appreciate your giving an example, so we can talk about it. Philadelpha to Lewes is about 120 miles, taking I-95. You pass right through Wilmington and Dover, and both have Superchargers. You wouldn't need to stop in both directions, but only one stop--either on the way there or the way back--would make this easy. With a four hour round trip, you can't fit in a 15-20 minute break on either side?

That's just the adjustment of assumptions and midset that make this easy if you can adapt to that. Instead of insisting on always being able to do 4-5+ hours non-stop, how about some willingness to take shorter segments with a couple of breaks here and there to use the bathroom, get a coffee, and then get back on the road? It's not bad.

Completely agree. After 48/49/50 cars and knocking on 50yrs old obviously i have a ton of built in habits. Gas stations on every corner, the comfort of fueling up and seeing 420 miles of range, being able to crank the AC to 58 (low) or heat to 90 and not worry about what its doing to my range or MPG. All old school ways of thinking.

What I do know is I haven't heard one single serious complain about their Tesla or range from any current owner. This includes family ( in CA), friends and work colleges.

The beauty and downfall of the internet is you can get on here and think out loud any irrational thoughts about pretty much everything.

Now comes the irrational thinking of if i wait a few more months the MY will be ever better....bigger battery, more range, some cool feature I'll never use.....battery day announcements.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,660
7,954
Boise, ID
Completely agree. After 48/49/50 cars and knocking on 50yrs old obviously i have a ton of built in habits. Gas stations on every corner, the comfort of fueling up and seeing 420 miles of range, being able to crank the AC to 58 (low) or heat to 90 and not worry about what its doing to my range or MPG. All old school ways of thinking.

What I do know is I haven't heard one single serious complain about their Tesla or range from any current owner. This includes family ( in CA), friends and work colleges.

The beauty and downfall of the internet is you can get on here and think out loud any irrational thoughts about pretty much everything.

Now comes the irrational thinking of if i wait a few more months the MY will be ever better....bigger battery, more range, some cool feature I'll never use.....battery day announcements.
I just got back last week from driving to visit my mom, and that is Boise, ID to Kansas City, MO--about 3,000 miles round trip, and I have one of the old 2014 Model Ses with about 250 miles of range and slower charging. I'm used to it, and I would be spoiled with the longer range and much faster charging of the Y or 3.
 

dmurphy

Buster: 11/25/14 - 6/20/21. So sorely missed.
Supporting Member
Dec 7, 2018
3,786
5,135
New Jersey - Morris County
Now comes the irrational thinking of if i wait a few more months the MY will be ever better....bigger battery, more range, some cool feature I'll never use.....battery day announcements.

Ahh.. the Osborne effect. Simply - forgoing today for the future possibilities is a never ending battle. Just jump in with both feet and enjoy every second of it!

(and PS - I don’t ever worry about the heat or AC. Comfort first....)

Keep in mind that for some people - many people on this board - efficiency and utilization is a game. They enjoy it. I don’t. I just want to drive the damn car. ;-)
 

Zoomit

Active Member
Sep 1, 2015
2,245
4,276
SoCal
You can charge your battery to 90% everyday if you prefer to do that. It is no big deal. I would recommend avoiding going below 15% or 12% unless you are really in a pinch.
Charging speed is not too important; Tesla knows what they are doing at superchargers.
It great to have experienced people weight in on best practices for Li-ion batteries. Here's another thread with some other generic but relevant advice: Battery Degradation Scientifically Explained.

As mentioned by @camalaio above, it is important to distinguish indicated SOC from actual SOC. These can vary by as much as 5%, based on my understanding of the low end buffer scheme that Tesla uses.

Advice directly from Tesla is obscure but exists. This Range Tips page says:
  • Maintain a regular, every-day charging routine using a low-voltage charger. It’s best to rely on high-voltage charging (i.e. Supercharging) only when necessary.
  • Whenever possible, don’t let the battery go above 90% or below 20%.
For long-term battery storage, Tesla states the following in EPA applications (page 17):
  • To maintain service life, the battery pack should be stored at a state of charge (SOC) of 15% to 50%.
(Note the distinction between 20% and 15% on the low end is likely because Tesla wants to keep you from inadvertently allowing your battery to completely discharge. The pack storage direction comes from a technical document and implies the pack is removed from the car and hence has no drain.)

Of course there's also Elon via twitter:
  • LikeTesla: @elonmusk any insight on the best nightly SoC for battery longevity? 90%, 70%, 50%? Any software fix for unbalanced cells due to sub 90% nightly charges?
  • Elon Musk: Not worth going below 80% imo. Even 90% is still fine. Also, no issue going to 5% or lower SoC
Plus Elon via twitter:
  • Tiko Hoppins: Its a rough estimate. You normally do not want to drain a Li-Ion battery below 15% of full capacity as over time it will reduce the cycle life much quicker than keeping it above 15%.
  • Elon Musk: A Tesla has a usable reserve of 5 to 15 miles range even after the battery reads “empty”. This will not hurt the pack.
All of this is in addition to the text in the Owners Manual section on battery care:
  • Model 3 has one of the most sophisticated battery systems in the world. The most important way to preserve the Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model 3 for several weeks. When plugged in, Model 3 wakes up when needed to automatically maintain a charge level that maximizes the lifetime of the Battery.
  • There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly.
  • The peak charging rate of the Battery may decrease slightly after a large number of DC Fast Charging sessions, such as those at Superchargers.
  • Never allow the Battery to fully discharge. Even when Model 3 is not being driven, its Battery discharges very slowly to power the onboard electronics.
  • For better long-term performance, avoid exposing Model 3 to ambient temperatures above 140° F (60° C) or below -22° F (-30° C) for more than 24 hours at a time.
 

camalaio

Active Member
May 28, 2019
1,483
2,106
Vernon, BC, Canada
... (Note the distinction between 20% and 15% on the low end is likely because Tesla wants to keep you from inadvertently allowing your battery to completely discharge. The pack storage direction comes from a technical document and implies the pack is removed from the car and hence has no drain.) ...

Not that I think this comparison actually happened, but the 15% vs. 20% might be due to open-circuit vs. load conditions. At low SoC, voltage sag is a lot more apparent (and the low cell voltage is what you're trying to avoid). So the 20% in the context of driving might be "similar" to open-circuit (not drawing power) storage of 15%. Approximately. Meh. I'm not convinced with my own argument, but it could be a factor. It's also unclear to me if 15% on the EPA doc is 15% of absolute capacity (how the EPA does tests), or 15% with a reserve buffer (how the car normally operates).
 

Zoomit

Active Member
Sep 1, 2015
2,245
4,276
SoCal
Not that I think this comparison actually happened, but the 15% vs. 20% might be due to open-circuit vs. load conditions. At low SoC, voltage sag is a lot more apparent (and the low cell voltage is what you're trying to avoid). So the 20% in the context of driving might be "similar" to open-circuit (not drawing power) storage of 15%. Approximately. Meh. I'm not convinced with my own argument, but it could be a factor. It's also unclear to me if 15% on the EPA doc is 15% of absolute capacity (how the EPA does tests), or 15% with a reserve buffer (how the car normally operates).
Yep, both good points.

I conclude, based on the variety of advice and guidance, that there’s no cliff in degradation when reaching any specific charge state. There’s just more incremental stress for the battery at lower SOC, as long as it’s above 0% SOC.
 

PhysicsGuy

Member
Apr 16, 2020
100
89
California
And I was getting to very close to buying a Y until i read the one sentence on here. Range is about 3hrs of highway driving......that doesn't sit well with me. I am in my car for hours a day with a varying commute, rarely going to the same place in the same order (sales). So if I am to get in my Y in Philadelphia and need to get to Lewes, DE, there may not be enough range to make it without stopping. I can make this drive easily now in my ICE car and can get to Lewes AND back on one tank with plenty to spare.

I am so on the fence about Tesla. Some days I feel like I am over thinking everything and other days my gut tells me something must be a serious concern of mine otherwise I would have bought a M3 years ago. This coming from someone who has owned 48 (or it is 49, 50) vehicles.
That is roughly 3 hours at 80 miles per hour. If you go slower you will get much more range! The model Y is a great car.
 

PhysicsGuy

Member
Apr 16, 2020
100
89
California
Not that I think this comparison actually happened, but the 15% vs. 20% might be due to open-circuit vs. load conditions. At low SoC, voltage sag is a lot more apparent (and the low cell voltage is what you're trying to avoid). So the 20% in the context of driving might be "similar" to open-circuit (not drawing power) storage of 15%. Approximately. Meh. I'm not convinced with my own argument, but it could be a factor. It's also unclear to me if 15% on the EPA doc is 15% of absolute capacity (how the EPA does tests), or 15% with a reserve buffer (how the car normally operates).
That seems like a very plausible and smart argument to me.
 
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PhysicsGuy

Member
Apr 16, 2020
100
89
California
Haha, thanks for taking it well! I had the exact same reaction as @Rocky_H :D


If I may nitpick a couple things for correctness though, since there's some technical details:
  • I'm not sure where your voltages come from, but mine are a bit different (mostly higher, even though not open-circuit). Are these generalised numbers for similar Li-ion cells? It seems like they might be, which doesn't quite match the displayed percentage for the Model 3. My numbers follow, close to 25C/77F:
    • ~4.15V @ 95%
    • ~4.12V @ 93%
    • ~4.08V @ 80%
    • ~4.00V @ ~72%
    • ~3.89V @ 60%
    • ~3.80V @ 50%
    • Any data I have for lower numbers is highly confounded (hot battery, too much power draw, etc.)
  • It's not always 46 parallel cells. See: Long Range vs. Mid Range vs. SR
  • Percent-to-miles doesn't work since battery size varies (see above).
I think an important-but-not-emphasised point in your post is this: "Tesla techs are not generally Li-ion battery experts". This is so, so incredibly unfortunate for the owners, especially when they hand-wave or blame the owner for bad charging practices that are actually good (sometimes even recommended by a different tech). We get mixed signals from different Tesla employees, Elon, folks on this forum, actual battery people, etc. At the end of the day (though people hate the comparison for some very valid reasons), you can often compare your phone battery to your car battery quite successfully since Tesla isn't that different in that regard. The differences bring up good discussion points.
The voltage differences are small, but interesting to me. What cell chemistry are your numbers for? There are probably more than 20 or 30 different 21700 size cells on the market now. I am not sure if the exact one that Tesla uses for the M3 is available for purchase. I think my numbers may have been for an MJ1 chemistry.
 
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