Every Other Day, Daily or Twice Daily Charging?

[Science fan]

This paper from NREL has some great info about calendar degradation. Based on this information I will try to keep the SOC of my Model S as low as is practical.

An HVB stored at 80% SOC and around 27 C will only last 10 years. An HVB stored at 60% SOC would have to be around 32 C to only last 10 years. At 27 C it will last much longer. The basic summary: keep the HVB as cool as possible & with the lowest SOC possible (within reason). Calendar degradation is going to be a larger part of total capacity loss than cycling degradation for most EVs. Keeping the HVB SOC as low as possible will add years to the lifetime of the HVB. The battery lifespan is defined as 80% of original capacity. However, don't let the SOC get too low, as this will damage the HVB due to increased stress on each cell as they have to provide the same amount of power with a lower voltage, thus necessitating higher amps (current) which causes more stress due to the internal resistance.

I plan to set my daily charge limit to 60%. If I expect to be driving more than about 75 miles in a day, then I will increase the charge limit so that I don't let the SOC (and thus the cell voltages) get too low. But ideally I will keep my SOC between 40% & 60% most of the time.

By managing the HVB SOC intelligently you can easily add 5+ years to your HVB lifespan. Considering the cost of the HVB, this seems like a smart move to me.

Good post, Hybridbear. The data you provide seems to be for an uncooled battery system. Is it true that our batteries are cooled while plugged in? If so, can we look forward to longer battery life, even if the ambient temperature averages 32 degrees C? Is there a standard temperature that our batteries are cooled to while plugged in?

 

[DFibRL8R]

Good post, Hybridbear. The data you provide seems to be for an uncooled battery system. Is it true that our batteries are cooled while plugged in? If so, can we look forward to longer battery life, even if the ambient temperature averages 32 degrees C? Is there a standard temperature that our batteries are cooled to while plugged in?

Yes the pack can be actively cooled or warmed depending on the scenario, all handled automatically by the battery management system of the car to optimize battery performance/longevity. Not sure about the target temps, I am in the plug and forget crowd . I believe some of these systems get disabled (or maybe just modified) when you put the car in range mode to extend range when necessary.

Not to complicate things but I also get the impression that keeping the car plugged in is better for the other battery in the car. You know the 12 V that runs all of the electronics in this computer on wheels. Due to the constant vampire drain of the computer systems in the Tesla that are on even when the car is in sleep mode, the 12V is subjected to frequent charge/discharge cycles which is not good for it's long term health. Full disclosure I am not an EE so I will let those who know more chime in. I believe keeping the car plugged in decreases the strain on the 12V. I am on my 3rd 12 V and in the "classic" model S it is not an easy DIY swap job so I want to keep mine happy.

 

[hybridbear]

Good post, Hybridbear. The data you provide seems to be for an uncooled battery system. Is it true that our batteries are cooled while plugged in? If so, can we look forward to longer battery life, even if the ambient temperature averages 32 degrees C? Is there a standard temperature that our batteries are cooled to while plugged in?

I definitely believe in plugging in whenever possible, but also in delaying charging as long as possible. I don't have a Model S yet to be able to look into 3rd party apps to monitor HVB temps.

 

[DFibRL8R]

I definitely believe in plugging in whenever possible, but also in delaying charging as long as possible. I don't have a Model S yet to be able to look into 3rd party apps to monitor HVB temps.

I am confused. How do you plug in whenever possible but delay as long as possible?

 

[hybridbear]

I am confused. How do you plug in whenever possible but delay as long as possible?

By using the delay charging feature built into the Model S.

 

[st50maint]

I did an experiment.
Charged my 70D to 190 miles.
Left it plugged in.
For 3.5 days the charge gradually decreased to 179 miles.
Then the car charged back up to 190 miles.
Apparently for 3.5 days the car did not do any charging.
So, for those 3.5 days, what would be the difference if plugged in or not?

 

[TexasEV]

By using the delay charging feature built into the Model S.

If you want to amuse yourself at home doing this, go right ahead, but I hope you aren't plugging in and delaying charging at destination chargers or other public charging stations. Do realize you're treating yourself and not the battery though.

 

[TexasEV]

I did an experiment.
Charged my 70D to 190 miles.
Left it plugged in.
For 3.5 days the charge gradually decreased to 179 miles.
Then the car charged back up to 190 miles.
Apparently for 3.5 days the car did not do any charging.
So, for those 3.5 days, what would be the difference if plugged in or not?

Here's what:
A connected Model S is a happy Model S

 

[DieAbetic]

Everyone needs to remember that while you are plugged in, the car is also not using the battery for the warming/cooling thermal management. This means the car is not putting any more cycles on your battery packs - it is getting that energy directly from the wall. Cycling the battery more definitely increases degradation no matter what battery study you look at - granted, it would be a very low/minimal impact because its only like 2-3 rated miles per day and the degradation is minimal in the first place. Nevertheless, it'll always be better for your car to be plugged in vs. sitting around using the battery to keep the perfect temp (especially if outside).

 

[kort677]

I am confused. How do you plug in whenever possible but delay as long as possible?

there is no reason to delay charging except if you live in a locale with timed service, where the electricity is lower cost at certain times.

 

[hybridbear]

The other key reason to delay charging is HVB temperature. As the NREL data shows, higher HVB temperatures accelerates calendar fade. The HVB heats up while driving to be warmer than ambient & heats up while charging. By delaying charging, you allow the HVB to cool back down close to ambient temp before it begins heating up again due to charging. You will avoid the hottest HVB temps by delaying charging. If you arrive home with a hot HVB from driving & then charge immediately, you will only push the HVB temp higher, causing more capacity loss.

If you want to amuse yourself at home doing this, go right ahead, but I hope you aren't plugging in and delaying charging at destination chargers or other public charging stations. Do realize you're treating yourself and not the battery though.

Why wouldn't you delay charging at Destination Chargers? Are you going to go move your car out of that spot in the middle of the night when it finishes charging? If not, then delaying the start of charging is a good idea.

there is no reason to delay charging except if you live in a locale with timed service, where the electricity is lower cost at certain times.

You are 100% wrong. Read the NREL study about the calendar degradation by SOC. Charging immediately means your HVB spends more time at a higher SOC & a higher temp (since charging raises the temp) which will lead to faster capacity loss.

A correct statement would be: there is no reason to charge immediately unless absolutely needed to continue driving.

 

[DFibRL8R]

The other key reason to delay charging is HVB temperature. As the NREL data shows, higher HVB temperatures accelerates calendar fade. The HVB heats up while driving to be warmer than ambient & heats up while charging. By delaying charging, you allow the HVB to cool back down close to ambient temp before it begins heating up again due to charging. You will avoid the hottest HVB temps by delaying charging. If you arrive home with a hot HVB from driving & then charge immediately, you will only push the HVB temp higher, causing more capacity loss.

Why wouldn't you delay charging at Destination Chargers? Are you going to go move your car out of that spot in the middle of the night when it finishes charging? If not, then delaying the start of charging is a good idea.

You are 100% wrong. Read the NREL study about the calendar degradation by SOC. Charging immediately means your HVB spends more time at a higher SOC & a higher temp (since charging raises the temp) which will lead to faster capacity loss.

A correct statement would be: there is no reason to charge immediately unless absolutely needed to continue driving.

I guess the best way to look at it is Tesla designed a sophisticated BMS so you don't have to think about it (though you can if you want to of course, just don't let your tendency to obsess about battery preservation infect the average owner who wants to just plug in and forget it). If the pack is hot, the car will actively cool it down whether you are charging or not. I have shown up at superchargers in the middle of a heat wave and plugged in after driving at high speed. The other parts on the Tesla seem to wear out faster than my main pack so I've stopped worrying about HVB at this point.

 

[kort677]

You are 100% wrong. Read the NREL study about the calendar degradation by SOC. Charging immediately means your HVB spends more time at a higher SOC & a higher temp (since charging raises the temp) which will lead to faster capacity loss.

A correct statement would be: there is no reason to charge immediately unless absolutely needed to continue driving.

was that study on generic ev batteries or on tesla batteries?
elon stated that a plugged in tesla is a happy tesla, I'll go with his views over some generic study.

 

[hybridbear]

I guess the best way to look at it is Tesla designed a sophisticated BMS so you don't have to think about it (though you can if you want to of course, just don't let your tendency to obsess about battery preservation infect the average owner who wants to just plug in and forget it). If the pack is hot, the car will actively cool it down whether you are charging or not. I have shown up at superchargers in the middle of a heat wave and plugged in after driving at high speed. The other parts on the Tesla seem to wear out faster than my main pack so I've stopped worrying about HVB at this point.

That may be possible, but no one has owned a Tesla long enough to know what the HVB life will be like over 6+ years.

was that study on generic ev batteries or on tesla batteries?
elon stated that a plugged in tesla is a happy tesla, I'll go with his views over some generic study.

I've never said not to plug the car in. You should absolutely plug in the car whenever possible. It's delaying charging, not delaying plugging in, that is the key to extending HVB life. I absolutely agree that the car should be plugged in whenever possible. But, plugging in to run active cooling for the HVB doesn't mean the HVB also needs to be charging at the same time.

You can read the NREL study to find out what battery chemistry, pack size, etc was tested. The results should extrapolate to other Li-ion batteries.

 

[Polly Wog]

As many up-thread have stated, just let the BMS do its job, and don't worry so much about it. I have a classic Model S 85, which was delivered with 265 miles of Rated Range. I currently have 29,000 miles (and 2 1/2 years) on my battery, and my Rated Range on a 100% charge has dropped all the way to 264 miles (yes, I've lost 1 whole mile!). I live in a condo (2nd floor) and charging my car has been challenging at times, so I don't charge every day. When I do charge, it is almost always to 90% (never less, if I can help it). Once a month, I charge to 100% to keep it "calibrated" (and yes, I then drive it shortly thereafter). Here on Maui, temperatures range from the mid-60's to mid-90's year round, so I've never really seen any seasonal change in my Rated Range. Lastly, my battery is very, very rarely below 50% SOC at any time, and spends 90% of its life above 60% SOC.

 

[TexasEV]

Why wouldn't you delay charging at Destination Chargers? Are you going to go move your car out of that spot in the middle of the night when it finishes charging? If not, then delaying the start of charging is a good idea.

Why wouldn't you? Well, for starters, you would be rude, inconsiderate, selfish, and other adjectives I won't use, in order to satisfy your obsession about the battery that would make an unmeasurably small difference over the life of the car.

Even if you don't have your Model S yet, you should know from your other EV that it's just plain wrong to plug into a public charging station and not charge! How'd would you feel if you arrived at a destination charging station to find that another Model S had been plugged in there for several hours but hadn't been charging because the owner was so self-absorbed that he was waiting for what he thought was the ideal moment to start charging his car.

These are shared resources. What you do at home with your obsession is your business, but don't go blocking public charging stations with a delayed charging start because of it.

 

[mikeash]

If you arrive home with a hot HVB from driving & then charge immediately, you will only push the HVB temp higher, causing more capacity loss.

I doubt that charging immediately after driving raises the temperature, especially if doing typical ~10kW home charging. Highway driving is draining 20kW or more on average, with many spikes, which I would think would heat the battery at least as much as charging. The battery is actively cooled, and if you drive home and then plug in, that active cooling will just keep on going while charging to keep the battery at the right temperature, if necessary.

 

[SBerg]

Thanks everyone!
Regarding plugging in while on vacation, I didn't while we were gone 21 days. HVB got down to probably 30% but when I went to drive the car, I got the 12V battery warning. Can't complain though, 68,000 miles and 33 months on the original 12V.

 

[hybridbear]

Why wouldn't you? Well, for starters, you would be rude, inconsiderate, selfish, and other adjectives I won't use, in order to satisfy your obsession about the battery that would make an unmeasurably small difference over the life of the car.

Even if you don't have your Model S yet, you should know from your other EV that it's just plain wrong to plug into a public charging station and not charge! How'd would you feel if you arrived at a destination charging station to find that another Model S had been plugged in there for several hours but hadn't been charging because the owner was so self-absorbed that he was waiting for what he thought was the ideal moment to start charging his car.

These are shared resources. What you do at home with your obsession is your business, but don't go blocking public charging stations with a delayed charging start because of it.

So when you're traveling in your Model S and reach a hotel with Destination Chargers you go & unplug your Model S & move it as soon as it finishes charging? What if you arrive at the hotel at 10 pm and the car is charging until 2 am? Are you telling me that you go & move the car at 2 am?!?!? If not, then there is no reason to have the car charge immediately. If you car is going to be parked overnight, then there's no reason to have charging start immediately.

I doubt that charging immediately after driving raises the temperature, especially if doing typical ~10kW home charging. Highway driving is draining 20kW or more on average, with many spikes, which I would think would heat the battery at least as much as charging. The battery is actively cooled, and if you drive home and then plug in, that active cooling will just keep on going while charging to keep the battery at the right temperature, if necessary.

Charging generates much more heat than discharging. Much of the heat generated during charging comes from the chargers that are stepping up the voltage. Charging creates way more heat than driving.

 

[mikeash]

Charging generates much more heat than discharging. Much of the heat generated during charging comes from the chargers that are stepping up the voltage. Charging creates way more heat than driving.

Heat from the charger doesn't go into the battery, so I don't see the relevance of that.