What should my ideal charge percentage be?

[TexasEV]

Why does Tesla still recommend charging between 50-90% via the slider?

Tesla doesn't recommend charging between 50 and 90% with the slider, it just makes it available. 50% is useful for long term storage. The slider was introduced several years ago to replace daily (92%) and trip (100%) modes so the EPA couldn't average the two together for rated range as it did with the Leaf.

 

[David99]

Someone mentioned that driving at a lower state of charge causes the battery to run hotter which would be a 'serious disadvantage'. With all due respect, but that's nonsense. With an app that monitors the input and output temperatures of each individual battery module I can say with 100% certainty that battery temperature has nothing to do with state of charge. There are several factors that affect battery temperature greatly, but the state of charge is not one of them.

Turning on 'Range mode', driving with lots of hard acceleration, Supercharging, driving in hot heather, driving constantly, charging at higher rates, driving uphill, ... all these things increase battery temperature. I have been keeping track of battery temperature for many months now. There is a lot of fluctuation and Tesla makes sure the battery is always in a healthy range without wasting much energy on heating or cooling the battery unnecessarily. Here is the theory: a lower state of charge requires a slightly higher current draw to achieve the same power level compared to a higher state of charge. Higher current draw causes slightly higher losses (=heat) but the difference is very small and negligible compare to the other factors at play. So while it is true that a lower state of charge decreases the efficiency slightly, it is too small to matter in reality.

Long story short, do not worry about charging to a lower level. It will not be bad for your battery due to heat. It is a proven fact that a lower state of charge will reduce battery degradation.

 

[apacheguy]

There's also an iPhone/iPad app called Remote S that has tons of features you can't get anywhere else (the developer is a Tesla owner and member of this forum with his own thread). With Remote S you can get even more granular 93,94,95% or whatever you want.

Remote S is not the only one. There are plenty of apps available including my own that make setting charge percent a breeze. It's a simple API call.

 

[msnow]

Tesla doesn't recommend charging between 50 and 90% with the slider, it just makes it available. 50% is useful for long term storage. The slider was introduced several years ago to replace daily (92%) and trip (100%) modes so the EPA couldn't average the two together for rated range as it did with the Leaf.

The Tesla DS's do tell new owners to charge daily to 90% though. I don't follow that but that's what they s

Remote S is not the only one. There are plenty of apps available including my own that make setting charge percent a breeze. It's a simple API call.

i was just pointing out the specific feature we were discussing and as you know Remote S has LOTS of features. What's yours called?

 

[TexasEV]

The Tesla DS's do tell new owners to charge daily to 90% though. I don't follow that but that's what they s

Yes and that's what I've always done. No good reason to charge any less. Even the car that usually charged to 100% for 200,000 miles has only lost 6% of range in that time. I've only lost 4% in more than 3 years of plugging in every night and charging to 90% (or 100% for trips). I'm very happy with that. Anyone who wants to baby the battery by charging it less, knock yourselves out, but you're treating yourself more than the battery.

 

[David99]

I've only lost 4% in more than 3 years of plugging in every night and charging to 90% (or 100% for trips). I'm very happy with that. Anyone who wants to baby the battery by charging it less, knock yourselves out, but you're treating yourself more than the battery.

Let me quote Professor Jeff Dahn who is now working with Tesla on battery development

I just had an interesting email exchange with Professor Jeff Dahn from Dalhousie University in Canada, who's a Lithium Ion battery expert (you can google his name or search him on YouTube and find his lectures). As a side note, one of his former Ph.D. students is now in charge of battery lifetime at Tesla.

Jeff's advice, which he was generous enough to give freely, and which I think comes with a great deal of authority, is this:

- In general, charge the battery to 80% unless you need more for a long trip. In fact, he said, 70% would be even better (the lower the upper cut-off voltage the cells see, the less electrolyte oxidation there is and the longer the lifetime will be).

- Discharging to 5% state of charge (95% discharge) doesn't harm the battery either. Discharging all the way, which could be damaging, is actually prevented by the Tesla pack control electronics. (I do know that Tesla advises against letting the battery charge run too low. I'm just guessing here that this is largely because they fear that people might miscalculate, run out of charge, and then we'll see pics posted online of Teslas being towed home. And nobody wants that.)

- Most interestingly to me, Jeff says that the number of charge cycles doesn't matter, only the accumulated charge capacity. As he put it, if you charge from 30% to 70% 150 times or from 10% to 70% 100 times, the aging of the battery will be approximately the same.

- Finally, while exposure to high temperatures isn't great for Li-ion batteries, the temperature of the Tesla pack is regulated by the car (even when parked), so it's not something owners need to worry about.

Yes and that's what I've always done. No good reason to charge any less. Even the car that usually charged to 100% for 200,000 miles has only lost 6% of range in that time.

'Charging to 100%' says only so much. What counts as well is the average state of charge over time. What the Tesloop cars do is charge and then go on the road right away. They do not stay on 100% for longer than a few minutes. To avoid long charge sessions with clients in the car, they most probably only charge just as much as they need when stopping in Barstow and arrive in Vegas at a rather low state of charge. So they cycle between 100% and 15%. That adds up to an average state of charge over time of just 57%.

 

[FlatSix911]

Good advice from an expert ... thanks

Let me quote Professor Jeff Dahn who is now working with Tesla on battery development:

I just had an interesting email exchange with Professor Jeff Dahn from Dalhousie University in Canada, who's a Lithium Ion battery expert (you can google his name or search him on YouTube and find his lectures). As a side note, one of his former Ph.D. students is now in charge of battery lifetime at Tesla.

Jeff's advice, which he was generous enough to give freely, and which I think comes with a great deal of authority, is this:
- In general, charge the battery to 80% unless you need more for a long trip. In fact, he said, 70% would be even better (the lower the upper cut-off voltage the cells see, the less electrolyte oxidation there is and the longer the lifetime will be).

 

[Galve2000]

I still say charge to 90%... set it and forget it....

 

[Acrono]

I have my charge limit set to 85% and never worry about it. I fully intend on dropping $35k in 4 years for a new battery (which may be a 120kWh+ based on brand new chemistry at that point). Babying a piece of technology that's already obsolete by the time you buy it is stupid IMO. I don't worry about my iPhone battery degradation for the same reason because I buy a new one every year.

Gotta pay to play. Simple cost of doing business.

 

[msnow]

I have my charge limit set to 85% and never worry about it. I fully intend on dropping $35k in 4 years for a new battery (which may be a 120kWh+ based on brand new chemistry at that point). Babying a piece of technology that's already obsolete by the time you buy it is stupid IMO. I don't worry about my iPhone battery degradation for the same reason because I buy a new one every year.

Gotta pay to play. Simple cost of doing business.

Comparing a ~$100k premium car to a $500 iPhone is not smart.
There's no reason to believe that 120 or 150 kWh battery you talk about will fit your car.

 

[Rodolfo Paiz]

Nice. Well with the 8.0 update, the adjusting charge is easier, ticks in 10% increments from 50-90%, then 2% from 90-100%. So easy to do a 94% charge every so often at least...

It's even better than that. The arrow buttons will do what you explained, but you can also touch and drag the charge line on the battery graphic itself, in 1% increments all the way from 50% to 100%. More flexible and easier to use.

 

[Rodolfo Paiz]

I have my charge limit set to 85% and never worry about it. I fully intend on dropping $35k in 4 years for a new battery (which may be a 120kWh+ based on brand new chemistry at that point). Babying a piece of technology that's already obsolete by the time you buy it is stupid IMO. I don't worry about my iPhone battery degradation for the same reason because I buy a new one every year.

Gotta pay to play. Simple cost of doing business.

You may freely choose how you operate your car, but please refrain from directing snide, condescending, and insulting remarks at those who choose differently, especially when it's so easy to pick apart your own arguments. For example, anyone could easily respond that "wasting money by unnecessarily degrading a battery's capacity is stupid" or that "intelligent cost control is among the most basic lessons of business survival". I could easily afford the $35K you quote for a new battery, but I'm much happier knowing that, with 98% of rated range still available on my battery after four years of ownership, I don't have to.

Be nice, please.

 

[Acrono]

Comparing a ~$100k premium car to a $500 iPhone is not smart.
There's no reason to believe that 120 or 150 kWh battery you talk about will fit your car.

Correct. In that case, you just buy another vehicle. So my analogy holds.

 

[Acrono]

You may freely choose how you operate your car, but please refrain from directing snide, condescending, and insulting remarks at those who choose differently, especially when it's so easy to pick apart your own arguments. For example, anyone could easily respond that "wasting money by unnecessarily degrading a battery's capacity is stupid" or that "intelligent cost control is among the most basic lessons of business survival". I could easily afford the $35K you quote for a new battery, but I'm much happier knowing that, with 98% of rated range still available on my battery after four years of ownership, I don't have to.

Be nice, please.

You're missing my point. My point is that battery technology, or rather, technology in general, advances so quickly that you shouldn't care about a degradation in range/capacity in 4-6 years because you'd want the next generation technology anyways that doesn't suffer from said drawbacks.

Here's another example in the computing space: people on enthusiast forums limit their CPU/GPU overclock frequencies because their die may last a few months shorter at 4.2 GHz versus 4.0 GHz (random.numbwr just used for example's sake). But since both would last at least 2 years, in the end, it doesn't matter (obviously substitute 2 years for 4-6 in the case of automotive battery technology).

PS: on a side note, intelligent cost control? Tell that to the finance/lending industry or the auto industry during 2007-2009 and how the US govt bailed them out despite poor "cost control". They all seem to have survived and are doing quite well now.

 

[msnow]

Correct. In that case, you just buy another vehicle. So my analogy holds.

Let's just say your analogy makes as much sense as the rest of your post. We can explain your lack of technical knowledge with you being a brand new owner but you'll have to live with your own financial choices. Please don't be rude to the poster because they are making smarter choices than you.

 

[Rodolfo Paiz]

You're missing my point. My point is that battery technology, or rather, technology in general, advances so quickly that you shouldn't care about a degradation in range/capacity in 4-6 years because you'd want the next generation technology anyways that doesn't suffer from said drawbacks.

Here's another example in the computing space: people on enthusiast forums limit their CPU/GPU overclock frequencies because their die may last a few months shorter at 4.2 GHz versus 4.0 GHz (random.numbwr just used for example's sake). But since both would last at least 2 years, in the end, it doesn't matter (obviously substitute 2 years for 4-6 in the case of automotive battery technology).

PS: on a side note, intelligent cost control? Tell that to the finance/lending industry or the auto industry during 2007-2009 and how the US govt bailed them out despite poor "cost control". They all seem to have survived and are doing quite well now.

I understand your point perfectly, I just disagree with it vehemently for various reasons:

1. You keep telling people what they should think or care about, and have no right to presume that your ideas are "better" in any way, either objectively or for any specific person other than yourself. You also dismiss those who think differently, which is inherently harmful and uncivilized (and won't do you any good, either, since you'll miss out on others' ideas, but that's your problem).

2. Your ideas are profoundly wasteful. My car's battery pack is 4 years old... that does not make it obsolete. Even if there's a pack with greater capacity out there in 1-2 years, or with better chemistry, that does not make it obsolete. It still goes 260 miles. It's probably good for a total of 15-20 years of driving, not 4-6 as you claim. And when I sell it, probably in 6-18 months, I care about handing over to its next owner a product that has not been unduly abused, will last a long time, and will not create unnecessary economic or environmental consequences. I like sustainability, civility, and courtesy. I like not treating things (or people) like they're expendable crap where I mistreat it and then just get another. I consider your recommendations fundamentally uncivilized, acting as though nothing matters but your own satisfaction shorn of any sense of responsibility, and as though when something leaves your hands it goes straight to the junk heap.

3. Your assumptions are flat-out wrong. I've driven Teslas now for nearly six years. The basic battery technology is exactly the same as it was six years ago, and it is not forecast to change dramatically for another 3-4 years at least. I have a bigger battery now in my Model S than I did in my Roadster. But bigger does not, in any way, mean technological improvements. There are no significant drawbacks to lithium-ion technology, nor have the real/perceived drawbacks changed in any way during this time. The lifecycle of a significant evolution in battery technology is more like 10 years, not 4-6. For instance, can you point to any technological drawback the Roadster's original battery had, that a new 100KWh Model S battery does not? Remember that range is not a technological drawback.

4. I'm not even going to touch your attempted rebuttal on cost control. Suffice it to say that, if you really believe the wasteful ideas you've espoused and have no faith in cost control as part of ANY and EVERY responsible business owner's toolkit, then God bless you because you're going to need His protection. I am not here to educate you.

 

[Acrono]

I understand your point perfectly, I just disagree with it vehemently for various reasons:

1. You keep telling people what they should think or care about, and have no right to presume that your ideas are "better" in any way, either objectively or for any specific person other than yourself. You also dismiss those who think differently, which is inherently harmful and uncivilized (and won't do you any good, either, since you'll miss out on others' ideas, but that's your problem).

2. Your ideas are profoundly wasteful. My car's battery pack is 4 years old... that does not make it obsolete. Even if there's a pack with greater capacity out there in 1-2 years, or with better chemistry, that does not make it obsolete. It still goes 260 miles. It's probably good for a total of 15-20 years of driving, not 4-6 as you claim. And when I sell it, probably in 6-18 months, I care about handing over to its next owner a product that has not been unduly abused, will last a long time, and will not create unnecessary economic or environmental consequences. I like sustainability, civility, and courtesy. I like not treating things (or people) like they're expendable crap where I mistreat it and then just get another. I consider your recommendations fundamentally uncivilized, acting as though nothing matters but your own satisfaction shorn of any sense of responsibility, and as though when something leaves your hands it goes straight to the junk heap.

3. Your assumptions are flat-out wrong. I've driven Teslas now for nearly six years. The basic battery technology is exactly the same as it was six years ago, and it is not forecast to change dramatically for another 3-4 years at least. I have a bigger battery now in my Model S than I did in my Roadster. But bigger does not, in any way, mean technological improvements. There are no significant drawbacks to lithium-ion technology, nor have the real/perceived drawbacks changed in any way during this time. The lifecycle of a significant evolution in battery technology is more like 10 years, not 4-6. For instance, can you point to any technological drawback the Roadster's original battery had, that a new 100KWh Model S battery does not? Remember that range is not a technological drawback.

4. I'm not even going to touch your attempted rebuttal on cost control. Suffice it to say that, if you really believe the wasteful ideas you've espoused and have no faith in cost control as part of ANY and EVERY responsible business owner's toolkit, then God bless you because you're going to need His protection. I am not here to educate you.

I'm not telling people what they should "think". I used the term "IMO" in my original post, which means, "In my opinion". Note the usage of pronouns in my original post: "I". I specifically didn't mention "you" or "the OP should do X".

Secondly, I disagree it's profoundly wasteful. Batteries and the lithium gets recycled. Even if it doesn't, the batteries will be tested and most, if not all of the cells will be used in a refurb battery (assuming degradation is in the low single digits).

Yes, in 5 or so years, actual battery technology hasn't changed much (though the battery packs have improved greatly). However, technology experiences exponential growth. As Tesla grows to 14k+ employees and hires the best engineers in the world, along with increased budget for R&D as their market cap grows, I think it's foolish to think batteries will advance on a 10 year cadence. But maybe I'm just being overly optimistic.

 

[Thesaint]

Im doing like 90% on week days and on weekends I normally give it a full charge.

 

[SteveGrey]

With all of this talk about ideal charge percentages, i'm curious where the software limited S60 fits into the mix. Since the current S60 has the 75 KWh battery and limits capacity (80 percent for you math majors), this changes the equation.

1. Does anyone know which 80 percent of the 75 KWh battery is used for the S60? My previous Volt had a 16 KWH battery limited to the 20-80% range for longevity. Does the Tesla limit the 75 pack to 0-80? 10-90? 20-100?

2. Depending on the charging range, does the battery management system change? If the battery is always kept below 90% by software, it would never reach the 93% leveling point.

3. If the battery is software limited above the true zero point, does the low battery "limp home" mode allow the car to dip into any of this reserve? I realize the software allows some reserve in all packs, but there could be significantly more if the engineers (or sales executives) wanted it to.

Thank you all for the insights, I'm hoping to buy an S60D when I move from Alaska. I traded in my Volt and replaced it with a bicycle (true zero emission vehicle) several years ago for my commute here in Kodiak, but my next duty station won't be as bike friendly.

 

[Canuck]

Anyone who wants to baby the battery by charging it less, knock yourselves out, but you're treating yourself more than the battery.

I don't get this. We're not getting up in the middle of the night to breastfeed our battery. We're just using our finger to slide the charge level slider a little lower when we don't need more for daily driving. We're not knocking ourselves out by doing it. It doesn't even cause me to breathe heavy it takes so little effort. My poor finger doesn't even get a workout.

Telling us there's no science behind it, by pointing to some vehicles and the manner in which a battery is rated by Tesla's software, as opposed to actually looking at the cathodes of the batteries, is like bringing a snowball into congress and saying there's no global warming. The science still stands for lower states of charge prolonging battery life. But even so, and even if you're right and we're just wasting our time, I haven't bathed mine, burped it, or taken it for a walk in a stroller. If I needed to do that to prolong battery life, you'd have a point.