Charing strategies for an infrequent driver that drives lots of miles

[Whisky]

* I'll preface this with stating my understanding that this is a largely academic discussion, and that no matter what charging strategy employed, battery degradation won't matter overly much across the 5 or so years I plan to own this car. I also have a MX75D but there are more people in the MS forum and it's the same battery type, so who cares?

I'm a fairly heavy driver (though probably a lightweight with some around here) at 15k miles a year, but I work from home, and live in a big city where I spend most days walking or taking transit when I'm not traveling.

So my driving goes something like this:

• Monday to Friday, almost no driving, or at most a few short occasional <10 mile drives
• Saturday and Sunday can reach 30 to 50 miles with errands, being out with family, friends, etc..
• Occasional I take planned in advance longer drives or road trips <- This part is the easy part, charge to 90% or 100% if you need it the night before, and done.

I've listened to some of the lectures with Dahn and he stresses the importance of temperature and discharge speed having the biggest affect on battery life.

Dahn states that discharging and charging can shorten the lifespan of a battery, but that the 30->70 is x-numbers less harmful than the 0->100. He also states that slow trickles of discharge are the best for the battery (so letting it vampire drain is better for the battery than driving the car, for example). And of course, he doesn't recommend charging beyond 70% if you don't need it, though we have some conflicting information here primarily around the TM3 battery and its issues with calibration unless you regularly charge to 80% or 90% (I don't have a TM3, so doesn't apply here). Dahn's advice isn't always based on the batter the Tesla MX and MS has, so it's always a little confusing as to what applies to us.

So using all that logic, my best practice is to let the battery naturally trickle down without any evening top-offs to bellow 50% (some would argue to bring it down to 30%, which makes sense I guess, but I'd like some mileage on the car in case of any unexpected driving). Once below 50%, charge it to 80%, and let it trickle down again.

I also realized, that instead of charging at midnight during the winter, it's probably best to charge the car immediately when coming home because the battery is already conditioned. If you charge at midnight, you're losing heat, wasting energy heating up the battery, before charging up. You're better off charging to (let's say) 70% from when you get home, and top it off to 80% an hour before you drive to head out with a warmer battery. I live in Canada, but my garage is fairly warm, so this isn't such a big issue for me.

So my strategy thus far has been, have a charged car by Saturday morning when I do most of my driving on the weekend, and let it trickle down to below 50% due to vampire drain (it usually doesn't get that low over the week anyway), and recharge again to 80%.

Am I missing anything? I'd love to hear your comments for those that obsess about these details.

* Also, I'll add the obvious, that the car is always plugged in! And I'm charging, not charing...

 

[TexasEV]

Am I missing anything? Yeah, you’re missing the fact that you don’t need a “charging strategy”. Let the battery management system manage the battery and just enjoy driving your car.

 

[Tslrsx]

The things you say make a lot of Sense but aren't really needed. Just plug in and charge to 90%(maybe 80 if you like to) and let the car take Care of itself. These batteries last for +15years, longer than the average car.

 

[wcorey]

* I'll preface this with stating my understanding that this is a largely academic discussion, and that no matter what charging strategy employed, battery degradation won't matter overly much across the 5 or so years I plan to own this car. I also have a MX75D but there are more people in the MS forum and it's the same battery type, so who cares?

I'm a fairly heavy driver (though probably a lightweight with some around here) at 15k miles a year, but I work from home, and live in a big city where I spend most days walking or taking transit when I'm not traveling.

So my driving goes something like this:

• Monday to Friday, almost no driving, or at most a few short occasional <10 mile drives
• Saturday and Sunday can reach 30 to 50 miles with errands, being out with family, friends, etc..
• Occasional I take planned in advance longer drives or road trips <- This part is the easy part, charge to 90% or 100% if you need it the night before, and done.

I've listened to some of the lectures with Dahn and he stresses the importance of temperature and discharge speed having the biggest affect on battery life.

Dahn states that discharging and charging can shorten the lifespan of a battery, but that the 30->70 is x-numbers less harmful than the 0->100. He also states that slow trickles of discharge are the best for the battery (so letting it vampire drain is better for the battery than driving the car, for example). And of course, he doesn't recommend charging beyond 70% if you don't need it, though we have some conflicting information here primarily around the TM3 battery and its issues with calibration unless you regularly charge to 80% or 90% (I don't have a TM3, so doesn't apply here). Dahn's advice isn't always based on the batter the Tesla MX and MS has, so it's always a little confusing as to what applies to us.

So using all that logic, my best practice is to let the battery naturally trickle down without any evening top-offs to bellow 50% (some would argue to bring it down to 30%, which makes sense I guess, but I'd like some mileage on the car in case of any unexpected driving). Once below 50%, charge it to 80%, and let it trickle down again.

I also realized, that instead of charging at midnight during the winter, it's probably best to charge the car immediately when coming home because the battery is already conditioned. If you charge at midnight, you're losing heat, wasting energy heating up the battery, before charging up. You're better off charging to (let's say) 70% from when you get home, and top it off to 80% an hour before you drive to head out with a warmer battery. I live in Canada, but my garage is fairly warm, so this isn't such a big issue for me.

So my strategy thus far has been, have a charged car by Saturday morning when I do most of my driving on the weekend, and let it trickle down to below 50% due to vampire drain (it usually doesn't get that low over the week anyway), and recharge again to 80%.

Am I missing anything? I'd love to hear your comments for those that obsess about these details.

* Also, I'll add the obvious, that the car is always plugged in! And I'm charging, not charing...

Well, per Ben Sullins "A plugged in Tesla is a happy Tesla".
Per Model 3 Owners Club @ecfix "charge to 80%".

 

[shred86]

While I understand the Tesla BMS is very good and following Tesla's simple recommendations are good enough for 99% of customers, I am also interested in learning about why they make the recommendations they do, understanding the details and assumptions behind those recommendations and also ways to further reduce battery degradation, regardless of how little it might be and the fact it will take several years to even see those differences. All that to say, I appreciate and enjoy these discussions.

I've also watched Jeff Dahn's videos, read some of the "Deterioration Analysis of Layered Lithium Nickel Oxide Based Cathodes for High Energy Density Lithium-Ion Batteries" doctoral thesis as well as a bunch of the articles on Battery University. The major points I've taken away for lithium-ion batteries in general:

• Maintaining cells at a voltage above 4.10V/cell degrades the battery.
• Combine the high voltage with high temperatures and it's even worse for battery degradation.
• Letting the battery get to very low SOC can also lead to degradation.
• A partial discharge and charge (also known as depth of charge) reduces stress and prolongs battery life.

The good news is the following the Tesla user manual/recommendations and having the awesome battery management system (BMS) mitigates most of these, but it's a balance between convenience and minimizing battery degradation for the majority of customers. So to answer your question, the fourth bullet aligns with Tesla's recommendation of simply keeping it plugged in. Not only will it reduce the depth of charge compared to waiting until your battery percentage is lower, it also helps minimize vampire drain since your Tesla will use grid power instead of battery power which ultimately leads to more cycles (I realize it's very minor but still a small point), which we know causes battery degradation.

You brought up a point I've been wondering about as well which is charging immediately after getting home or setting a charge schedule that finishes just before you leave (assuming cold temperatures). Although I agree with your point about using less energy since you're not wasting energy heating up the battery packs before starting to charge, I think you could also make the argument your efficiency is better driving with a battery pack that is closer to optimal temperatures and you get full regenerative braking. There are obviously many variables that make it difficult to quantify but what I'm more curious about is what is better for reducing battery degradation. We know that charging in very cold or hot temperatures is not good for lithium-ion batteries but Tesla's BMS manages this (it will heat or cool the battery pack before charging), but it's obviously setup to balance convenience with battery longevity. In other words, I doubt it's waiting to get to the best temperature before (best being defined as the least amount of battery degradation) beginning to charge. Otherwise, it would probably take a long time in some climates before you get any charge. Again, I realize the difference here is probably very minimal and wouldn't really be seen unless you kept the car for a long time, but still something I'm curious about.

The other part I can't find a great answer on is why the recommendation is 70% from Jeff Dahn. Supposedly JB Straubel has mentioned 50-62% in the past but I'm not sure what exactly these recommendations are based on. This article on Battery University states, "A cell voltage of 3.92V appears neutral; lower voltages add to SEI, higher to EO", SEI being solid electrolyte interface and EO being electrolyte oxidation, both of which are the cause of battery degradation. I think the recommendation from Jeff Dahn is close to that 3.92V for a Tesla at 70%, but I don't know for certain. I've also read the idea of keeping battery levels centered around 50% which I think comes from JB Straubel's recommendations, but I'm also not sure why although one person mentioned in the Tesla forums that "the closer to 50% the better because thats the least amount of cell voltage change from when you charge." As for long term storage, I've read the recommendation of 50% and keeping it plugged in, but again, I don't know why when the article I mentioned above suggests 3.92V is the best state for your battery.

Anyways, would love to hear from other folks that are smart on this subject.

TLDR: As the OP state, this is largely an academic discussion. Don't bother reading unless you're actually curious about why battery degradation occurs. Simply following Tesla's recommendations is good enough for the majority of owners.

 

[P85_DA]

Your overthinking this

 

[TexasEV]

@Whisky and @shred86, hypothetically five years from now my car (charged to 90% every night and 100% for trips) may have 295 mile rated range and your cars may have 297 mile rated range. I hope those additional two miles are meaningful for you.

 

[shred86]

As I already mentioned, I'm well aware that following Tesla's recommendation is perfectly fine for 99% of users. This is largely an academic discussion and very few people will find benefits in going beyond simply following Tesla's recommendations (ownership for 5+ years and/or high mileage owners... maybe and it will still be fairly minimal). And since you brought it up, comparing rated miles isn't really the best metric for measuring battery degradation. Obviously not worth going into the details since you probably don't care, but it's something I see often mentioned in these discussions. Despite being a broken record, I'll say it again. Tesla's BMS is great and their recommendations work fine. No one is questioning that. My questions/discussion are mostly for my own edification.

 

[wcorey]

I'm well aware that following Tesla's recommendation is perfectly fine for 99% of users.

Isn't that rather elitist, implying you're in the advanced percentile of Tesla owners that really are talking way over the head of the mere mortals? What is it in your driving profile that places you in this elite class? I am sure you don't intend the but your posts drip, on this subject, with contempt. As Tesla does not provide cell battery voltage or amperage isn't your thesis mere fanciful guessing that can never be empirically proved or disproved? I am pretty certain internally Tesla does know the internal state of the cells and their recommendations are based on that plus years of research by PhD's who do that for a living. To imply, "yes, but some of us are more discerning" fall apart when you have no scientific evidence to make any claims? The advise of Tesla is 80%, the advice of Eric Camacho of Model 3 Owners Club is an unequivocal 80%, ditto with Ben Sullins. There was no caveat of 'for most users'. Although for long occasional trips, fully charge.
From the Model 3 Owners Manual: emphasis is theirs

About the Battery
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.
Note: When left idle and unplugged, your
vehicle periodically uses energy from the
Battery for system tests and recharging the
12V battery when necessary.
There is no advantage to waiting until the
Battery’s level is low before charging. In fact,
the Battery performs best when charged
regularly

 

[bob_p]

With 6 years of experience with 2 Model S and 1 Model X - our best charging advice to other owners is to KEEP IT SIMPLE...

If possible, when not driving, stay plugged in - with charge level set no higher than 90%. The battery will slowly lose a little charge, and then periodically recharge back to 90%.

While investing time in optimization of the charging level or rate might result in a small reduction in battery degradation, it doesn't appear to have a significant benefit.

Keep it simple...

 

[hacer]

I like to get the grill really hot first - run the flames at max with the lid closed for 12 minutes or so. Then make sure you've oiled the food and place it in the center of the grill, close the lid, leave it (still on max) for a minute, then flip over the food, close the lid for another minute. After those two minutes the food is charred at that point. You can turn down the heat and finish cooking, open the lid, or raise the food higher from the grill depending on your cooking preference.

 

[shred86]

Isn't that rather elitist, implying you're in the advanced percentile of Tesla owners that really are talking way over the head of the mere mortals? What is it in your driving profile that places you in this elite class? I am sure you don't intend the but your posts drip, on this subject, with contempt. As Tesla does not provide cell battery voltage or amperage isn't your thesis mere fanciful guessing that can never be empirically proved or disproved? I am pretty certain internally Tesla does know the internal state of the cells and their recommendations are based on that plus years of research by PhD's who do that for a living. To imply, "yes, but some of us are more discerning" fall apart when you have no scientific evidence to make any claims? The advise of Tesla is 80%, the advice of Eric Camacho of Model 3 Owners Club is an unequivocal 80%, ditto with Ben Sullins. There was no caveat of 'for most users'. Although for long occasional trips, fully charge.
From the Model 3 Owners Manual: emphasis is theirs

Apologies if that’s how you took it, but I was trying to emphasis that most vehicle owner probably drive somewhere between 10-15k miles a year and probably will move to a new vehicle in 5-10 years, so Tesla’s recommendations are great. The other 1% would be folks who plan on keeping for 10+ years or drive more than the average, say 30-50k+ miles a year, which I don’t even know if that’s 1% of the user base but I was just trying to emphasis it’s a very small group.

As for voltage, I’m referencing that based on what those articles I linked to state, and voltage is what actually used in studies rather than percentage since that varies (depends on the EV/electrical device). And yes, Tesla obviously can read the voltage of each cell and I’m pretty certain their recommendations are based on a percentage that translates to a voltage. You can actually see the voltage of each cell pack but it requires reading data off the CAN bus which there are apps like TM-Spy or Scan My Tesla that can do this.

As I’ve stated three times now, I understand what the recommendations are and realize they work great. I’m simply trying to understand the why behind those recommendations. If you truly believe 80% is the perfect number to minimize battery degradation in all conditions, then there’s no point in even getting involved in these discussions. Tesla is not going to recommend some ridiculous charging strategy because at some point, convenience and ease of use significantly outweighs the very minor benefits the typical driver would see. A 1% average degradation a year is a very minor trade off to be able to provide a very easy and user friendly charging recommendation. Could you imagine if the recommendation was something like, “When it’s >X degrees outside, charge to 50% once the battery temps reach Y degrees at rate of Z kW/hr, but when it’s <X degrees outside, charge to 70%....” all to reduce

So to summarize, all I’m trying to understand are things like “Why does Jeff Dahn recommend 70%?, “Why does Eric Camacho and Eric Sullins recommend 80%?”, “Why is 50% recommended by Tesla (service center) for long term storage?”

 

[wcorey]

You can actually see the voltage of each cell pack but it requires reading data off the CAN bus which there are apps like TM-Spy or Scan My Tesla that can do this.

Thanks! I did not realize there were 'deep dive' apps beyond Tezlab (of which Ben Sullins does not hesitate he is on the board of). I assumed you were referring to people in a lab environment seeing actual cell behavior under test conditions where all variables were controllable. Then too, there is the issue of which batteries, S and X or Model 3?

 

[shred86]

Those apps require an adapter cable that plugs into your OBD2 port then another device that allows you to pair with your mobile device, like the LELink 2 Bluetooth adapter. There’s a bunch of data you can view and log such as battery voltage of each cell pack, temperature, actual state of charge (different than what’s displayed in the car), actual battery capacity, etc. Some folks were able to discover things like cell balancing doesn’t occur until >93%, range mode actually increases battery temperatures to increase range efficiency, the displayed energy use only accounts for when the car is moving and not at a stop, etc. Definitely gee-wiz stuff, but just interesting to learn about (for some).

I’m sure @TexasEV will jump on here and remind me that it’s simple as “Charge to 90% and keep it plugged in. A plugged in Model S is a happy Model S”. I know and it really is that simple. If you look at some of the other threads, he’s like a broken record but I understand why. There’s many people who see some of these threads, think they’re now doing something wrong and begin overthinking it without every having even read the user manual which will tells you what to do in capitalized font. But, there’s also those of us that simply want to learn (i.e. understand the why behind things) and/or perhaps make some minor adjustments for their own reasons. I’ve always used discussion board to have, well, discussions and I thought since the OP prefaced his post with a disclaimer that this would be an appropriate place to get into the details.

Anyways, found this post which a user actually emailed Jeff Dahn and got a response which I thought was pretty cool. Mostly the same information as he mentions in his lectures but goes into a little more detail.

 

[Uncle Paul]

Perhaps the answer to your questions is that, because there are so many variables, it is difficult to answer your question of which specific charging system "is best" at any given point in time.

Tesla is constantly improving the density, cost, configuration, size, alloys used, chemical proportions and types. They have integrated many different battery packs and different versions of each. They have many different cooling systems and assembly proceedures. They also have offered many different charging systems and control systems. Their battery control algorithms have been modified many times and will continue to be improved as technology marches on.

You are asking forum members to tackle all this and tell you which charging philosophy will absolutely work our for you in your uncertain future, with different driving conditions and temperatures every day.

It is a pretty big ask...

 

[dark cloud]

I liken this to someone wanting to get either maximum life or efficiency by experimenting with tire pressures. For most people we go with what is recommended by the manufacturer. Of course we the owners are the TMS (tire management system). Run the tire down to 0 psi and it damages it. Over inflate it and it damages it.

Others do some experiments and try to see the differences between 45 psi vs 44 or 45.5 psi to get another 0.7Wh/mi of range or 100 miles of tire life. There are too many other variables to consider and as the OP suggests if it’s +- 1% of a difference 99% of us don’t care. Nothing wrong with inquiring minds though.

 

[Whisky]

@Whisky and @shred86, hypothetically five years from now my car (charged to 90% every night and 100% for trips) may have 295 mile rated range and your cars may have 297 mile rated range. I hope those additional two miles are meaningful for you.

I like yeah and all but I think the concept of “largely academic” is escaping your notice. Literally the first paragraph stated doesn’t actually matter for the duration of my planned car ownership. No need to keep stressing the point that the discussion was founded around and acknowledged.

 

[Whisky]

The other part I can't find a great answer on is why the recommendation is 70% from Jeff Dahn. Supposedly JB Straubel has mentioned 50-62% in the past but I'm not sure what exactly these recommendations are based on. This article on Battery University states, "A cell voltage of 3.92V appears neutral; lower voltages add to SEI, higher to EO", SEI being solid electrolyte interface and EO being electrolyte oxidation, both of which are the cause of battery degradation. I think the recommendation from Jeff Dahn is close to that 3.92V for a Tesla at 70%, but I don't know for certain. I've also read the idea of keeping battery levels centered around 50% which I think comes from JB Straubel's recommendations, but I'm also not sure why although one person mentioned in the Tesla forums that "the closer to 50% the better because thats the least amount of cell voltage change from when you charge." As for long term storage, I've read the recommendation of 50% and keeping it plugged in, but again, I don't know why when the article I mentioned above suggests 3.92V is the best state for your battery.

Thanks for participating in this and offering some terrific feedback!

I do wonder if part of the magic behind Telsa’s BMS is the management of voltage across battery blocks so that when one charges to 80%, not every cell is at 80% (that’s most certainly true anyway), but rather some get charged up to 90% while others are resting at a lower state like 70%, and based on performance, the BMS makes adjustments on individual blocks. Does that even make sense? I feel like these technical dives cover a lot of information, but little is spoken of how the BMS actually works.

 

[Rocky_H]

In other words, I doubt it's waiting to get to the best temperature before (best being defined as the least amount of battery degradation) beginning to charge. Otherwise, it would probably take a long time in some climates before you get any charge.

Well, I can address this part, and it's kind of in between. The "otherwise", which you seem to think is a rhetorical that doesn't happen, is exactly what happens in some circumstances, though. People who have connected to something like a low power J1772 station that was only supplying 30A have had it do no charging at all for sometimes a half hour or entire hour if it was far below freezing. It's doing nothing but run the battery heater with that 30A for quite a while first.

The way you stated this shows that you're thinking of it in a binary state:
0 = too cold = no charging
1 = warm enough = charge as fast as possible

It's not like that, because it's a gradual sliding scale of how many amps the battery can safely charge at based on temperature. There is a temperature point below which it is just too cold, and there can be no charging without damage. And the Tesla cars do prevent charging at those temperatures, unlike most other electric cars. But it can get up to a temperature where it can do some slow charging that is below the damage threshold, and that keeps rising to allow more amps as the temperature continues to get higher. That is illustrated in the progress of no regen versus limited regen versus full regen. That is what rate of charging it can allow based on temperature.

 

[shred86]

@Whisky The only thing I've read and seen in videos on the BMS is that the balancing circuit engages when charging reaches 93%. Once it's active, the balancing process will continue (regardless of charge level) until it's complete, which could take multiple days. This was discovered by wk057 somewhere in this thread (so many pages, I forgot where I read about it).

@Rocky_H Ah yeah, that makes sense and now that I think of it, I've seen that mentioned several times (charging "throttles back" when it's cold).