What's your 90%?

[wdolson]

As someone with roughly the same mileage and stats (238 at 90%, 263 at 100%) on a 2014 P85 with rev. D battery, I'm curious about something: how often do you plug your car in?

I plug in maybe twice a week, when needed. Yes, I know we've been told that "a plugged-in Tesla is a happy Tesla," but I normally don't leave the car plugged in for longer than it takes to charge. My battery shows very little degradation (when new, it was 240 at 90% and 265 at 100%), and I'm still on my original 12V battery after 3 years.

Could it be that many short charging cycles are actually not as beneficial as fewer overall cycles, and/or avoiding the low end of the battery's range? (I don't know; it's something I'm wondering based on my experience.) Maybe there's a behavioral component, or maybe some people just get luckier with their chemistry.

I think it's just some people get luckier than others. My mid-2016 S 90D had 270 miles at 90% Thursday. It's usually 268 and sometimes 269. It's rare I see 270, but I did bump up the charging to 91 or 92% once a few days ago. It's back to 90% now.

The car sometimes sits for a couple of days without being driven and it's always plugged in at home. When vampire loss had dropped the range to 265 or 266, I sometimes top off the charge to 269 before leaving.

I supercharged a few times last summer and fall and had a long road trip in October, but I haven't been to a supercharger since I got back from that trip. So much has been going on here we haven't gone anywhere that required a charge to get home. I rarely get below 200 miles range.

 

[Markk993]

to answer your specific question i plug in when needed so about once every 5 days and there is a supercharger in the parking lot of my favorite restaurant so more often than not I just go and get an appetizer if i am out and about. So I plug in (home or otherwise) charge up to 234 and drive it all week until it gets to about the 50-60 mile range...


Not sure if that is good or not but for the 15 months that I have had the car it is still at 234 @ 90% so I assume that I am not harming anything...

i am sure there will be some that tell me that this is not the best way but that is what I have been doing

 

[Brass Guy]

to answer your specific question i plug in when needed so about once every 5 days and there is a supercharger in the parking lot of my favorite restaurant so more often than not I just go and get an appetizer if i am out and about. So I plug in (home or otherwise) charge up to 234 and drive it all week until it gets to about the 50-60 mile range...


Not sure if that is good or not but for the 15 months that I have had the car it is still at 234 @ 90% so I assume that I am not harming anything...

i am sure there will be some that tell me that this is not the best way but that is what I have been doing

Maybe someone will, but 20%-90% is probably quite healthy for the battery.

 

[SmartElectric]

2013 S85 VIN 6xxx with original "A" battery pack revision
60000 miles
230 miles @ 90%
256 miles @ 100% (~3% degradation)

Charged to 90% daily and 100% (yes, 100%) at least once per week, twice per week in winter, sometimes left at 100% for half a day, sometimes a few hours, depends. Supercharged dozens of times on roadtrips to 100%, run down to 7% many times on roadtrips.

So : "Keep calm", just charge and drive. YMMV IMHO Whatever

 

[jerry33]

Could it be that many short charging cycles are actually not as beneficial as fewer overall cycles, and/or avoiding the low end of the battery's range?

If this is true, then Tesla batteries work the opposite of every other Lion battery. 4.5 years, 94.5K miles 297 Ideal miles at 100%. (300 when new). Plug in daily (okay, I've forgotten about twice). Charge to 100% when going on a trip.

 

[holtz13]

2013 P85
58,500 miles
230 @ 90%

 

[SMAlset]

We usually only charge to 80% but did a 90% before starting out on a trip and got 226 on our 2017 75D.

 

[charansr]

90% - 266 miles
down 1 mile (267) in 5 months

2017 90D 3500 miles 5 months

 

[thecloud]

If this is true, then Tesla batteries work the opposite of every other Lion battery...

Wikipedia says that rechargeable lithium-ion battery lifetime is measured in a number of charge/discharge cycles before significant capacity loss occurs. Degradation is divided into "calendar loss" (chemical reduction of electrolyte over time) and "cycling loss" (reduction due to usage, with variation depending on the minimum/maximum charge states and depth of discharge.) High cycling rates, such as frequent supercharging would produce, will cause fissures in the anode and subsequent capacity loss.

So, if I compare my battery to someone else's battery of the same calendar vintage and assume they have similar chemistry at the outset (which may itself be a flawed assumption!), the main difference will be the cycling loss. There are other factors, such as temperature, which come into play, but there would still seem to be a strong correlation between range loss and lots of charging cycles.

What I was wondering was whether any advantage existed to cycles that are fewer in number but slightly deeper (as in my case and @Markk993 where we plug in weekly), versus cycles which are smaller but more frequent (as in your case where you plug in daily). Since we both have seen little degradation, there's probably little difference.

I suspect it's more important to avoid low states of charge, and to charge at lower rates (I normally charge at 30-32 amps).

 

[jdw]

Shallow cycles tend to be better for lithium battery life ...

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.”

 

[thecloud]

Thanks for that info, @jdw. I think the depth of discharge was a critical piece of the equation that I was missing.

Say I routinely charge to 90%, and then drive until the battery is about 50%, at which time I plug in and do one charge cycle from 50% to 90%. Elapsed time here might be 4 days. Alternatively, I could drive daily from 90% down to 80%, plug in every night, and be back up to 90%. So in the same period, I would either do 1 charge cycle, or 4 charge cycles.

In the first case, DoD is 40%, and in the second, it's only 10%. But the 10% is offset by having to do 4 times as many charge cycles. However, if I understand the chart correctly, you can do 5 times as many short cycles (replacing 10% lost SoC) as longer ones (replacing 40% at a time) across the life of the battery. So I think I'm convinced that I should start doing opportunistic short charges.

 

[S100D]

My 2016 S90D was delivered on December 27 last year. I was getting 267 miles at 90% until a month ago. I took a 4,500 mile month long vacation. My odometer is now at around 7,500 miles and 90% is now 261 miles. I talked to the Service Center last week and told them I lost 6 miles in a month and as normal they said that it is not a problem. During my vacation, I never charged it to 100%.

I had a 2015 S85D and did not lose that many miles in a year. I will do a 100% charge soon to see if that helps.

 

[wdolson]

"“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.”

True, except if you are discharging to 50% and then recharging, on a car with a 300 mile range, that would be about 150 miles of charge each session and the life of the battery would be around 180,000 miles for 1200 cycles. Otherwise, I agree. Individual battery packs are going to be better than others though. I've seen 0% degradation in a year when others who have done the same thing have seen 5%.

 

[jerry33]

True, except if you are discharging to 50% and then recharging, on a car with a 300 mile range, that would be about 150 miles of charge each session and the life of the battery would be around 180,000 miles for 1200 cycles. Otherwise, I agree. Individual battery packs are going to be better than others though. I've seen 0% degradation in a year when others who have done the same thing have seen 5%.

I suspect driving style has a bearing on this as well.

 

[jdw]

Thanks for that info, @jdw. I think the depth of discharge was a critical piece of the equation that I was missing.
...
In the first case, DoD is 40%, and in the second, it's only 10%. But the 10% is offset by having to do 4 times as many charge cycles. However, if I understand the chart correctly, you can do 5 times as many short cycles (replacing 10% lost SoC) as longer ones (replacing 40% at a time) across the life of the battery. So I think I'm convinced that I should start doing opportunistic short charges.

I think the key concept is "Cycle life improves faster than DoD reduces,", so yes, it would seem to me that short cycles and opportunistic charging is the way to go. Since heat and state of charge also play into it, a pattern like:

Daily usage 10-20%:

1) Set timer to charge to 90%, finishing just before you leave for work
2) Drive to work (car sits ~8 hours at 90% minus the drive)
3) Drive home (car sits ~14 hours at 90% minus two drives)

With higher usage, it makes sense to charge around a lower charge % number perhaps opportunistic charging to 80% while out and about in the heat.

This is close to my actual pattern and my 85D 90% after two years/19K miles is 103% of delivery or 270 miles/range mode off so, it seems to be working so far / I got lucky.

It would likely be even better to cycle around the mid-point (50-60%) but I found the rated battery range got out of whack charging below 90% and my average state of change doing what I do is about 75% anyway.

 

[Viking1]

Thanks for that info, @jdw. I think the depth of discharge was a critical piece of the equation that I was missing.

Say I routinely charge to 90%, and then drive until the battery is about 50%, at which time I plug in and do one charge cycle from 50% to 90%. Elapsed time here might be 4 days. Alternatively, I could drive daily from 90% down to 80%, plug in every night, and be back up to 90%. So in the same period, I would either do 1 charge cycle, or 4 charge cycles.

In the first case, DoD is 40%, and in the second, it's only 10%. But the 10% is offset by having to do 4 times as many charge cycles. However, if I understand the chart correctly, you can do 5 times as many short cycles (replacing 10% lost SoC) as longer ones (replacing 40% at a time) across the life of the battery. So I think I'm convinced that I should start doing opportunistic short charges.

From what I've read it is not the number of charges that is a cycle, but the total charge. Charging from 0 to 100 would be one cycle. Charging 10% at a time for 10 times is also one cycle.

I was letting my battery go down to 10% then charging to 90%. I was losing about 1 RM/week doing this. I now charge at every chance. I think I may have done permanent damage to my battery. I've lost about 4% in 9 months and 9K miles. Tesla said a plugged in Tesla is a happy Tesla. I now understand why.

 

[SmartElectric]

You haven't damaged your battery. Lithium Ion cells degrade up to 5% within the first half year or year, and then slowly degrade thereafter. After two years, our 2013 S85 was 3% degradation, in the 2.5 years since, nothing lost.

Our routine is to charge to 100% Friday evening prior to weekend trips and 90% daily.

It's my wife's car, she does not believe in "babying" the battery, if she wants to go on a trip, the car is charged to 100%, and if the battery can't take it, the car needs to be traded in. Can't argue with that logic.

 

[wdolson]

I suspect driving style has a bearing on this as well.

Historically I am a bit of a lead foot, but I do tend to take good care of my stuff. The guy I sold my 1992 Buick to (last December) commented on how good the interior looked. Except for some carpet wear it looked virtually new inside.

 

[dgpcolorado]

I suspect driving style has a bearing on this as well.

Perhaps also where one lives. When driving steep hills the power draw is much higher for a given speed than driving in the flatlands, even when not driving aggressively.

 

[jdw]

From what I've read it is not the number of charges that is a cycle, but the total charge. Charging from 0 to 100 would be one cycle. Charging 10% at a time for 10 times is also one cycle.

I was letting my battery go down to 10% then charging to 90%. I was losing about 1 RM/week doing this. I now charge at every chance. I think I may have done permanent damage to my battery. I've lost about 4% in 9 months and 9K miles. Tesla said a plugged in Tesla is a happy Tesla. I now understand why.

Exactly - at 90% discharge & charge, you might get something like 5-600 cycles before you're into serious degradation (say 200mi x 500 cycles = 100,000 miles). Doing 5 times as many 20% discharges gets you something like 9000 cycles x 40 miles or 360,000 miles.

Nobody is going to drive like that every day, but you can see the effect of deep discharging and the benefit of smaller cycles and frequent charging.