What should my ideal charge percentage be?

[wayner]

"Remember, a connected model S is a happy Model S."

Do you mean connected as in Wifi/LTE/3G or connected as in plugged in for charging? These days I would argue that connected is used more for the former than the latter.

Given this discussion of charging strategies it would be nice if the scheduler would let you schedule a charge end time, assuming a given charge rate. I have written some code to do this as in the winter I would like my charging to end as near as possible to 7 am which is when my electricity rate goes up and is about the time I leave for work. That helps to minimize any regen limits.

 

[msnow]

Do you mean connected as in Wifi/LTE/3G or connected as in plugged in for charging? These days I would argue that connected is used more for the former than the latter.

Given this discussing of charging strategies it would be nice if the scheduler would let you schedule a charge end time, assuming a given charge rate. I have written some code to do this as in the winter I would like my charging to end as near as possible to 7 am which is when my electricity rate goes up and is about the time I leave for work. That helps to minimize any regen limits.

He and the manual are speaking about plugging in but I think being Internet connected is a good thing too.

 

[TexasEV]

Do you mean connected as in Wifi/LTE/3G or connected as in plugged in for charging? These days I would argue that connected is used more for the former than the latter.
.

Plugged in.

The quote isn't mine, it's Tesla's. The Model S used to be delivered with a postcard in it with a picture of the car plugged in and that quote. I wish they still did that-- it might save a lot of questions.

 

[Larry Hutchinson]

Still includes that postcard.

Must say I am a skeptic, though and don't bother.

 

[TexasEV]

Still includes that postcard.

Must say I am a skeptic, though and don't bother.

Then they started including it again, which is a good thing. They hadn't for a long time-- hence all the questions-- or perhaps it was placed where people didn't see it.

 

[CarlitoDoc]

Interesting thread. I did learn quite a bit. I don't believe I read any posts related to folks (like me) that have super-short daily commutes (mine is about 10-15 miles roundtrip). I will be using my EV (CPO Model S or Model 3....still on the fence) for long trips on weekends (150 miles) about twice a month. So the question is: What % charge would you set for daily charging? Thanks for the input.

 

[Larry Hutchinson]

I have a 4 mile round trip and set my charge to about 60%.

 

[TexasEV]

Interesting thread. I did learn quite a bit. I don't believe I read any posts related to folks (like me) that have super-short daily commutes (mine is about 10-15 miles roundtrip). I will be using my EV (CPO Model S or Model 3....still on the fence) for long trips on weekends (150 miles) about twice a month. So the question is: What % charge would you set for daily charging? Thanks for the input.

I would set it at 90% and never think about it again.

 

[Past Gas]

If you ever run out of charge, this is what you do:
(Sorry folks, I was on my way to see the Falcon 9 reusable rocket next door to the Hawthorne superchargers and back-tracked here because I had to take this picture of this poor guy!)

 

[ToddRLockwood]

Given the introduction of the "slider" I would like Tesla to give a number (percentage charge) that is optimal for the life of the pack. If you never (or almost never) need the full, or even standard charge range; what is the best level to charge to on a daily basis? Most driving days for me are less than 30 miles. What's my number? I'm certain it wouldn't totally end speculation. If Tesla engineers came up with a number for this scenario it would end any speculation for me.

I traded up to a 2016 90D this summer, and with a brand new battery I was inspired to dig into the charging question again. There is surprisingly little official information about the "ideal" daily charge level for long battery life. So I consulted an expert I know inside Tesla, as well as an outside engineer who does charging-related consulting for Tesla. Here's the scoop...

The Model S and Model X battery has an automatic balancing routine that is triggered when the battery is charged to 78% or higher. If the battery is repeatedly charged to a lower level over a long period of time, the cell modules will become out of balance with one another, leading to pack that runs hotter.

A charge cycle is defined as a full charge from about 3 volts to 4.2 volts per cell. If your car is about half full and you charge it to 100% that is considered to be half a cycle and has less than half the impact on your battery health than a full cycle. It's much easier on your battery health to perform many small cycles than a few deep cycles. Tesla recommends charging your battery every day for a reason. It's better for battery longevity.

Charging your battery to below 80% every day (for example 60%) provides little or no benefit and a couple of serious disadvantages. The first and biggest issue with only charging to about 60% everyday is that you are constantly driving your car at a lower voltage. Why is that bad? Because everything runs hotter at a lower voltage. Your battery's biggest enemy is heat. Driving every day at a lower state of charge will cause it to always run hotter and consequently degrade faster. Your motor(s) and power electronics will also run hotter which causes them to wear out sooner as well. Charging to only 60% every day is better for your cell phone, but not your car.

The other problem with only charging to 60% every day is your battery will often be out of balance. The reason that's bad is the cells wear out unevenly. Cells at a lower state of charge will heat up more than others while driving and consequently wear out quicker. Since the whole pack is only as good as the lowest performing cell group, wearing one of them out quicker degrades the whole pack quicker. Therefore it's important to charge your car high enough that automatic balancing kicks in on a regular basis.

Bottom line: 80% is the ideal daily charge, and you should plug in as often as possible.

 

[FlatSix911]

I traded up to a 2016 90D this summer, and with a brand new battery I was inspired to dig into the charging question again. There is surprisingly little official information about the "ideal" daily charge level for long battery life. So I consulted an expert I know inside Tesla, as well as an outside engineer who does charging-related consulting for Tesla. Here's the scoop...

The other problem with only charging to 60% every day is your battery will often be out of balance. The reason that's bad is the cells wear out unevenly. Cells at a lower state of charge will heat up more than others while driving and consequently wear out quicker. Since the whole pack is only as good as the lowest performing cell group, wearing one of them out quicker degrades the whole pack quicker. Therefore it's important to charge your car high enough that automatic balancing kicks in on a regular basis.
Bottom line: 80% is the ideal daily charge, and you should plug in as often as possible.

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

 

[msnow]

I traded up to a 2016 90D this summer, and with a brand new battery I was inspired to dig into the charging question again. There is surprisingly little official information about the "ideal" daily charge level for long battery life. So I consulted an expert I know inside Tesla, as well as an outside engineer who does charging-related consulting for Tesla. Here's the scoop...

The Model S and Model X battery has an automatic balancing routine that is triggered when the battery is charged to 78% or higher. If the battery is repeatedly charged to a lower level over a long period of time, the cell modules will become out of balance with one another, leading to pack that runs hotter.

A charge cycle is defined as a full charge from about 3 volts to 4.2 volts per cell. If your car is about half full and you charge it to 100% that is considered to be half a cycle and has less than half the impact on your battery health than a full cycle. It's much easier on your battery health to perform many small cycles than a few deep cycles. Tesla recommends charging your battery every day for a reason. It's better for battery longevity.

Charging your battery to below 80% every day (for example 60%) provides little or no benefit and a couple of serious disadvantages. The first and biggest issue with only charging to about 60% everyday is that you are constantly driving your car at a lower voltage. Why is that bad? Because everything runs hotter at a lower voltage. Your battery's biggest enemy is heat. Driving every day at a lower state of charge will cause it to always run hotter and consequently degrade faster. Your motor(s) and power electronics will also run hotter which causes them to wear out sooner as well. Charging to only 60% every day is better for your cell phone, but not your car.

The other problem with only charging to 60% every day is your battery will often be out of balance. The reason that's bad is the cells wear out unevenly. Cells at a lower state of charge will heat up more than others while driving and consequently wear out quicker. Since the whole pack is only as good as the lowest performing cell group, wearing one of them out quicker degrades the whole pack quicker. Therefore it's important to charge your car high enough that automatic balancing kicks in on a regular basis.

Bottom line: 80% is the ideal daily charge, and you should plug in as often as possible.

The BMS (Battery Management System) kicks in at 93% charge not 78%. So, to keep your battery in balance occasionally charge to 93%. When you first get your car the Delivery Specialist usually recommends plugging in every day and charging to 80-90% daily. Personally, I only charge when it gets around half empty (40-60%) and it works for me.

 

[ToddRLockwood]

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

Good question. Charging beyond 80% when needed would certainly make sense, although I try to avoid 100% charges altogether. We have enough Supercharger locations in New England that it's rarely necessary to charge beyond 80%. And as my previous post mentions, it's better for the battery and more time-efficient to charge more often. The rate of charge begins tapering above 80% and slows even more above 90%.

As for charging to a level below 80%, there may be situations where it would be useful, but you'd want to get back to the 80% percent level for the long term, so your battery will be getting re-balanced regularly.

When I took delivery of my first Model S, a 2013 P85, there were no Superchargers in New England. To make trips to Boston from Burlington, Vermont I had no choice but to charge to 100% occasionally. Otherwise, I charged to 90%. At 50,000 miles, my P85 had lost about 7% of its range, which Tesla told me is typical. But I had heard of other owners who had little or no range loss at 50,000 miles, and I began wondering what they were doing differently.

 

[ToddRLockwood]

The BMS (Battery Management System) kicks in at 93% charge not 78%. So, to keep your battery in balance occasionally charge to 93%. When you first get your car the Delivery Specialist usually recommends plugging in every day and charging to 80-90% daily. Personally, I only charge when it gets around half empty (40-60%) and it works for me.

I'm no expert. Just passing along the information I received. Where did you find out about the 93% level for auto-balancing?

 

[Dave EV]

the cell modules will become out of balance with one another, leading to pack that runs hotter.

I'd love to see some actual data backing this up. Unless you're constantly flooring it, I suspect the difference in temperature will be negligible.

Because everything runs hotter at a lower voltage.

Same as above.

 

[apacheguy]

I charge to 75% daily and I monitor cell voltage spread. My pack is in perfect balance with a spread of only 4-6 mV.

 

[msnow]

I'm no expert. Just passing along the information I received. Where did you find out about the 93% level for auto-balancing?

1. wk057 (our resident battery expert around here).
2. Tesla Service always asks me to do a 100% charge when they want me to calibrate rated range but according to wk 93% will do it.
3. Personal experience - you can actually see the impact on your rated range/percentage gauge for a couple of days after you trigger the BMS.

 

[travwill]

1. wk057 (our resident battery expert around here).
2. Tesla Service always asks me to do a 100% charge when they want me to calibrate rated range but according to wk 93% will do it.
3. Personal experience - you can actually see the impact on your rated range/percentage gauge for a couple of days after you trigger the BMS.

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...

 

[jerry33]

I'm no expert. Just passing along the information I received. Where did you find out about the 93% level for auto-balancing?

WK57 did a lot of testing with Model S parts on the bench and discovered that battery balancing is triggered at 93%. Once triggered it runs until balancing is complete regardless of charge level. This may take several days. This was on an 85 kWh battery. If you have information that's different for the 90 or 100 kWh battery, that would be useful information for those owners.

 

[msnow]

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...

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.