Charging frequency and battery life

[jerry33]

interesting, so then my revised options are as follows:

1) Set slider to 50% 6 of 7 days of the week, 90% on day 7
2) Set slider to 90% every night

Which is better for the battery health?

Well, I tried 80% for a couple of years, and the miles shown went down. The last two years I just set it to 90% and the number went back up (slowly, and with a few 95%-100% charges). Now at 4 years 5 months and 94K miles, I estimate it is just under 3% down from new. Plugging it in more often--daily for me--is likely to do more good than keeping the charge low, unless you are storing the car for an extended period (read months). The reason for this (as far as I know) is that when driving the car, a higher number (90% to 50%) is better than a lower number (20%-50%).

The basic recommendation is don't overthink it, just drive it. I only do four things:
1. Set the charge limit to 90%
2. Set the timer so that the charge finishes about the time I start driving.
3. When going on a trip, I do a full charge before leaving (or close to a full charge depending upon how well I've timed it).
4. If there is a long gap between trips, I'll charge to 95% on a day when I anticipate a lot of driving (pack balancing circuits turn on at 93%).

 

[Ugliest1]

Well, I tried 80% for a couple of years, and the miles shown went down. The last two years I just set it to 90% and the number went back up (slowly, and with a few 95%-100% charges). Now at 4 years 5 months and 94K miles, I estimate it is just under 3% down from new. Plugging it in more often--daily for me--is likely to do more good than keeping the charge low, unless you are storing the car for an extended period (read months). The reason for this (as far as I know) is that when driving the car, a higher number (90% to 50%) is better than a lower number (20%-50%).

The basic recommendation is don't overthink it, just drive it. I only do four things:
1. Set the charge limit to 90%
2. Set the timer so that the charge finishes about the time I start driving.
3. When going on a trip, I do a full charge before leaving (or close to a full charge depending upon how well I've timed it).
4. If there is a long gap between trips, I'll charge to 95% on a day when I anticipate a lot of driving (pack balancing circuits turn on at 93%).

This is exactly my experience. Kept it at 80% the first couple of years max rated reduced to about 6%+. Changed to 90% 1-1.5 years ago, max rated miles gradually went up until last 6 months degradation at about 4.5%, except for the last 100% charge on Tuesday showing only a 3% degrade.

Could be tweaking the RM calculator more than recovered battery health, but I'm not worried about it. I do #1, 2, and 3 above.

 

[jerry33]

This is exactly my experience. Kept it at 80% the first couple of years max rated reduced to about 6%+. Changed to 90% 1-1.5 years ago, max rated miles gradually went up until last 6 months degradation at about 4.5%, except for the last 100% charge on Tuesday showing only a 3% degrade.

Could be tweaking the RM calculator more than recovered battery health, but I'm not worried about it. I do #1, 2, and 3 above.

I check using ideal miles because that doesn't seem to change the way rated miles does.

 

[David99]

I just found the forum message where a member gave some info about battery degradation that came directly from Jeff Dahn who is working with Tesla on battery development.
Read here

- 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.

Quick note about the discharge to 5%. When you discharge your Model S or X to 0%, there is actually a few percent left in the battery. Based on the CAN bus data it's aprox 5%. In other words it is totally fine, from a battery health point of view, to drive the car to 'zero'. Of course in real life that isn't smart because you might not make it to your next charger, but it's not bad for the battery.

 

[SureValla]

I just found the forum message where a member gave some info about battery degradation that came directly from Jeff Dahn who is working with Tesla on battery development.
Read here

- 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.

Quick note about the discharge to 5%. When you discharge your Model S or X to 0%, there is actually a few percent left in the battery. Based on the CAN bus data it's aprox 5%. In other words it is totally fine, from a battery health point of view, to drive the car to 'zero'. Of course in real life that isn't smart because you might not make it to your next charger, but it's not bad for the battery.

wow that seems to disagree with the overall theory in this thread, point 1 above about setting as low a upper cut-off as possible seems the be the best for the health of the battery. This would also seem to disagree with the idea that a plugged in battery is a happy battery...

 

[Veritas1980]

Even though there is a lot of debate about this, and various school of thought on the subject, I take comfort in noticing that there is almost no complaints here on sudden loss of range. And at lot of those there are, seems to be due to faults in the battery pack, often covered by the warranty.

So to me, that seems to indicate that the packs will most likely keep pretty well, either one way or another.

There are of course exceptions to this, but generally speaking.

Personal, I like the theory, that David99 quoted, seems to line up with what I read other places on Lithium batteries. But I have faith in Tesla's know-how on this subject. If we where all doing something wrong, I would assume they would make changes to the firmware or give new recommendations for charging.

 

[David99]

wow that seems to disagree with the overall theory in this thread, point 1 above about setting as low a upper cut-off as possible seems the be the best for the health of the battery. This would also seem to disagree with the idea that a plugged in battery is a happy battery...

The recommendation to keep your car plugged in isn't about battery health at all. It's teaching owners to always plug in their cars, because if you forget, your car isn't charged and you end up not being able to drive where you want to. That is a far more frustrating experience than 1% more degradation after 2 years. Look at how most people drive their cars or charge their phones. They wait until it's almost empty and then they think about filling it up and charging it. That doesn't work for an EV. It takes many hours to charge. Hence the recommendation to always plug it in when parked and use the idle time to charge it. Always topping it off making sure owners don't run out of juice. But it is not good for the battery.

There are several things that are bad for the battery but good for every day use/performance. For example temperature. The battery performs best at pretty high temperatures, but it causes more degradation. A cold battery will show far less degradation but perform poorly and have less capacity.
Charge level is the same. A low charge level is best for longevity, but only charging a battery 40% gives you far less range.
Fast charging is awesome for road trips but a fast charge rate will cause more degradation.

 

[TexasEV]

The recommendation to keep your car plugged in isn't about battery health at all. It's teaching owners to always plug in their cars, because if you forget, your car isn't charged and you end up not being able to drive where you want to.

That's not what Tesla said. Here is a photo of the card Tesla used to provide in the cars at delivery:
A connected Model S is a happy Model S

The current "quick reference manual" says something similar:
"We recommend plugging in Model S every day. The most important way to preserve the battery
is to leave your Model S plugged in when you are not using it."

It doesn't say it's to preserve the owner's sanity, it says it's to preserve the battery.

 

[jdw]

Meanwhile, over at "Battery University", there is an article on what affects lithium battery longetivity/

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

 

[TexasEV]

You can't extrapolate everything you read about batteries to Tesla batteries, because the cars manage the battery temperature.

 

[jdw]

FYI, a CleanTechnica article on the subject as it relayes to EV's/

Battery Lifetime: How Long Can Electric Vehicle Batteries Last?

"Cycle life improves faster than DoD reduces, so that the total charge transferred is greater at lower depth of discharge.

This is significant, because it means that a larger battery used at less than full discharge can be more economic and last longer than a smaller capacity battery used at full depth of discharge."

and

"“Of course, as Battery University explains, it’s not as simple as that. After 300 to 500 cycles at 100 percent depth of discharge, a lithium-ion cell’s capacity will drop to 70 percent. But partial discharge “reduces stress and prolongs battery life.” Drain the batteries consistently to only 50 percent, as is often the case with electric cars that get plugged in frequently, and life expectancy of a healthy battery zooms up to 1,200 to 1,500 cycles. That, of course, translates to 366,000 miles, but don’t expect numbers like that on your odometer. Other wild cards such as frequency of fast recharge can also affect battery life.”

 

[Ugliest1]

The recommendation to keep your car plugged in isn't about battery health at all. It's teaching owners to always plug in their cars, because if you forget, your car isn't charged and you end up not being able to drive where you want to. That is a far more frustrating experience than 1% more degradation after 2 years. Look at how most people drive their cars or charge their phones. They wait until it's almost empty and then they think about filling it up and charging it. That doesn't work for an EV. It takes many hours to charge. Hence the recommendation to always plug it in when parked and use the idle time to charge it. Always topping it off making sure owners don't run out of juice. But it is not good for the battery.

There are several things that are bad for the battery but good for every day use/performance. For example temperature. The battery performs best at pretty high temperatures, but it causes more degradation. A cold battery will show far less degradation but perform poorly and have less capacity.
Charge level is the same. A low charge level is best for longevity, but only charging a battery 40% gives you far less range.
Fast charging is awesome for road trips but a fast charge rate will cause more degradation.

I would say you are describing extremes. Your statements are truthful, but not useful (IMHO!).

For example, last sentence "fast charging ... more degradation" may be technically true, but I'm thinking it's not enough degradation to actually be concerned about. If you buy the car and just let it sit there, never driving it for fear of degrading the battery, the battery will STILL degrade slightly -- that is also a true, but not useful statement. These things were made to be used.

 

[SureValla]

Disclaimer: Yes I realize the following is extremely nitpicky and the end result probably doesn’t matter much. Some may call my investigation fretting over nothing or claim that I am stressing out without much gain. However, being an engineer the details are extremely interesting to me and optimizing my charging is something I enjoy and can assure you, does not cause me to lose sleep at night.


I think everyone here can agree that plugging in every night is something that should be done and I can’t see how the mere act of connecting the cable could hurt the battery. If anything this potentially helps the battery as if you use the app to turn on the climate control the car will use the grid energy rather than taxing the battery.


The question that is up for debate is whether the car should be charging when connected and to what % it is best to charge it to.


Charge to 100%: Everyone agrees this hurts the battery and the longer the car spends at full charge the more it will be hurt. The advice seems to be that if you really need the 100% to schedule your charge such that you pull out of your driveway as soon as the car ticks over from 99% to 100%. Commentary: With the supercharger network getting so great I can’t honestly see a reason to need to go to 100% vs. say 90%. I think I’d rather make a 5 minute stop at a SC than harm my battery by going the extra 10%.


Charge to 90%: This seems to be the general recommendation from tesla for the masses. It’s an easy catch all # that won’t hurt the battery the way 100% will. This setting balances real world use and battery health.


Charge to 80%: From the post above the battery expert states this is better for the battery health than 90% but you won’t see the same improvement that you would going from 100% to 90%.


Charge to 70%: From the post above the battery expert states this is better for the battery health than 80% but you won’t see the same improvement that you would going from 90% to 80%.


Charge to 60%: Though not specifically stated I would imagine the logic for 80% and 70% applies here as well although. However, at some % reduction you see diminishing returns in terms of increasing battery health.


Charge to 50%: Same logic as 60%


Charge to <50%: Not possible per the software limitations


The consensus also seems to be the batteries have a limit to how many cycles they can go through (1 cycle being charging from 0% to 100%). Therefore the act of charging the batteries damages them.


However, there seems to be a damage multiplier depending on the end charge percent. This can be seen by the fact that charging from 50% to 60% (1/10th of a cycle) does not cause as much damage as charging from 90% to 100% (also 1/10th of a cycle). It can therefore be inferred that the higher you charge the more damage you do per cycle.


I should also add though that keeping the care at low charge percentages is also bad. I would estimate below 10%. I have not found an explanation at this time though for why this is the case.


Conclusions:

Based on the logic above and if all you care about is battery health, I see no reason to set the charge limit above 50%. For all practical purposes the range degradation over time between setting 50% or 90% seems to be minimal and probably easily offset by the times charging to 90% will get you through unexpected trips where you may need the extra 40%. Another option would be to just use the SC network to offset the inconvenience that charging to 50% may cause. You can easily fix the mistake with a 15 min stop at your local supercharger.


Another consideration, and the reason I find this topic interesting, is for people that only need to plug in once per week or in my case can get a free charge once per week. Are these people worse off than those who charge daily? I can’t see a reason this would be the case as it’s only the act of charging the “hurts” the battery. The only guidance here would be to avoid low states of charge (<30% and definitely <10% may be a good guideline).


Finally, because of the excellent SC network, I see no reason to ever exceed 90% (as I commented in the 100% section).

 

[TexasEV]

Finally, because of the excellent SC network, I see no reason to ever exceed 90% (as I commented in the 100% section).

Real world Tesla driving experience disproves this.

 

[SureValla]

Real world Tesla driving experience disproves this.

Interesting comment. Can you elaborate? My thinking is lets say you have a long trip coming up. Giving yourself an extra 10% won't really get you there that much faster.

Lets say 100% is 250 mi for my example. 90% is 225 mi and giving yourself a buffer of not dipping below 10% it reduces it to 200 mi.

All trips under 200 mi are good to go
All trips from 200-225 mi now require 1 SC stop they didn't require when charging to 100%
All trips under from over 225 mi would have required a SC anyway.

I can understand once you start getting into really long road trips (i.e. 1000 mi) you may have more of an argument that charging to 100% would save you a lot more time.

 

[TexasEV]

You're describing ideal scenarios. Not every trip has a supercharger en route and not every destination has convenient level 2 charging. Also you're equating rated range with actual range. Trips on rural interstates take much more range than rated range (speed limits of 80 mph are common in the west) and driving into headwinds or in rain cuts range even more. Etc., etc.

 

[SureValla]

You're describing ideal scenarios. Not every trip has a supercharger en route and not every destination has convenient level 2 charging. Also you're equating rated range with actual range. Trips on rural interstates take much more range than rated range (speed limits of 80 mph are common in the west) and driving into headwinds or in rain cuts range even more. Etc., etc.

ahh ok makes sense then. In my area the SC is much more built out so diverting to one is much more possible. Plus things are closer in general than they are out west, a long trip for me rarely exceeds 3-4 hours drive time, NYC, Boston, Phily are all within that time range and so many SC along the way you could probably even skip every other one.

 

[Ugliest1]

... so many SC along the way you could probably even skip every other one.

But why would you want to skip any? Most Superchargers Visited

 

[David99]

For example, last sentence "fast charging ... more degradation" may be technically true, but I'm thinking it's not enough degradation to actually be concerned about.

We all are aware that after a certain amount of Supercharging or DC charging the car will reduce your charge speed. Tesla officially admitted it after some users found out. The discussion here caused concern among a lot of owners here. So I think it's worth being aware of.

 

[Ugliest1]

We all are aware that after a certain amount of Supercharging or DC charging the car will reduce your charge speed. Tesla officially admitted it after some users found out. The discussion here caused concern among a lot of owners here. So I think it's worth being aware of.

Sure... as far as I know that's only for the early 90 packs?