Is a standard charge significantly worse than an 80% charge?

[kjl]

Hi; I was dumb and didn't really give myself a lot of leeway regarding battery capacity and range, so loss of capacity over time will be bad for me. Oops.

I know a range charge (100%) is worse for your battery life than a standard charge (90%), and I assume 90% is worse than 80%, and 80% worse than 70%, etc., but my question is "how much worse?" Part of the joy of this car in comparison to other EVs is not having to worry about range. If charging to 80% saves me 1% of battery capacity after 100,000 miles then its not really worth it, but if it saves me, say 5% after 50,000 miles, then I'd probably bite the bullet and go through the trouble of charging to 80 or 70 and adjusting every night if I plan on a trip the next day or something.

Apologies is this question has been asked before.

P.s. I know the S hasn't been around so long that people will have empirical evidence about this; I think I'm asking the question to people who know anything about battery technology in general. If charging to 90% for 100,000 miles is expected to decrease battery capacity by X%, then charging to 80% for 100,000 miles would be expected to decrease battery capacity by what%? i.e. where does the diminishing returns on charging less every night get to the point where it's not worth the hassle anymore?

 

[FlasherZ]

Tesla feels comfortable telling you to charge to standard / 90% on a daily basis and I'd put a lot of faith in that.

That said, if you can comfortably get by with less, it is likely to be better for the batteries. As to how much? I'd suggest you not trade off worry of the difference there for range anxiety. Lithium-Ion batteries are happiest somewhere near 50% SOC, but don't put yourself in a bad situation.

(Today a local town experienced 5 inches of rain in less than an hour, which forced me to delay and re-route my path home as water rushed over the highway. It forced me about 10 miles out of my way, along with the rain-driving penalty that drives my usage up by 75-100 Wh/mi, and I returned home with 29 miles of range. Leave yourself some headroom.)

 

[kjl]

Lithium-Ion batteries are happiest somewhere near 50% SOC, but don't put yourself in a bad situation.

For me, my daily usage is either ~40 miles or ~140 miles (not much in between) so it's not really a case of me trying to charge exactly the the correct level or having range anxiety. 50% would be plenty, easily, on the days I do 40 miles. The "trouble" would just be remembering to switch it back and forth between 50% and 90% every night when I get home. I'm pretty lazy and would much rather just do 90% every single night and never think about it again, but if it gains me an extra 50,000 miles of battery life to do it I'd suck it up.

I have a feeling 90% is the right answer. Thanks.

 

[100thMonkey]

I try to stick with mid pack cycling but I'm not driving typically 140 miles a day. in your case, I'd stick with standard and simply set the charge timer to have it completed close to when you are leaving in the morning, to minimize the amount of time the car sits at a high SOC. from what I've read, it's having it sit at a high SOC that's really the issue.

For me, my daily usage is either ~40 miles or ~140 miles (not much in between) so it's not really a case of me trying to charge exactly the the correct level or having range anxiety. 50% would be plenty, easily, on the days I do 40 miles. The "trouble" would just be remembering to switch it back and forth between 50% and 90% every night when I get home. I'm pretty lazy and would much rather just do 90% every single night and never think about it again, but if it gains me an extra 50,000 miles of battery life to do it I'd suck it up.

I have a feeling 90% is the right answer. Thanks.

 

[jerry33]

Bear in mind that there will be degradation with age even if you never drive it, so you can't reduce degradation to zero. Also heat is a factor. So the worst conditions are hot and very high or very low SOC. I suspect but don't have any data to back this up, that even a small amount down from 100% gets a big reduction in degradation while from 90% to 70% only gets a moderate amount of reduction.

As a practical matter, what I would do, if I had 4.5 and was very concerned about battery life, would be to charge to the lowest SOC that gets me:

1. Three days plus 10% normal driving (In case of power outage or charging problems).

2. 90%.

3. So that after a day's driving SOC is not below 40% (low SOC is particularly bad if you also drive spiritedly).

But I doubt that there is all that much difference in battery life between doing that and just charging at 80% to 90% and not worrying about it.

 

[kendallpb]

My daily drive is about 50 miles, plus potential unexpected errands; weekends, I might do more or less (usually less); once or twice I've let my other half use the car, so this may result in more usage than originally planned, as I will probably "allow" this more and more.

Anyway, after obsessing about this and being pretty grumpy, I finally compromised on 80%. (shrug) No doubt, I could go lower, but I've set up timed charging so that I'm up at 80% for a shorter time each day. So now that I'm "letting" my other half use the car occasionally, I'd rather not have to worry about reverting to charging at every plug-in or whatever. 80% was my compromise amount; I figure, if I'm actually taking a trip, I'll almost certainly range charge, so I'd be unlikely to forget and leave it at 80%.

 

[dirkhh]

Tesla tells you to leave the car plugged in whenever you aren't driving it. And they set the default to 90% (down from 93% in earlier firmware version).

Given that they provide warranty for the battery, I'd be very surprised if there was a dramatic improvement in battery life by going down to 80%. If that was the case, Tesla would have a "storage mode" or something that keeps the car at a lower charge level.

So unless someone has hard data (not random "I read somewhere that batteries do better at 50%") that relates to the Tesla battery design... I see no reason whatsoever to charge to anything but the default 90%.

 

[brianman]

This is another example of where superchargers help BTW. For example, if your home is (for simplicity...) directly between 4 superchargers (one at each compass point) then when you go on a roadtrip you'll only have half the distance to a supercharger (maybe we need a unit for this...) at most to travel to fill up if you decide to go on a road trip suddenly.

 

[kendallpb]

Tesla tells you to leave the car plugged in whenever you aren't driving it. And they set the default to 90% (down from 93% in earlier firmware version).

Given that they provide warranty for the battery, I'd be very surprised if there was a dramatic improvement in battery life by going down to 80%. If that was the case, Tesla would have a "storage mode" or something that keeps the car at a lower charge level.

So unless someone has hard data (not random "I read somewhere that batteries do better at 50%") that relates to the Tesla battery design... I see no reason whatsoever to charge to anything but the default 90%.

I went down to 80% partially due to Tesla's contradictory messages--they say both "charge to the level you need, 50-90%, lower is better" and "leave it at 90% is fine." I figure a little lower, based on their confusing statements and what I read around here, isn't a bad idea. But yeah, I expect little-but-perhaps-not-zero benefit from doing this and no harm from doing this. Every little bit helps and I finally admitted I don't need the 25-30 mile difference from 80-90% and I realized won't stress me out not to have it. But everyone's different. I don't need even 50% of the battery, daily, but I would never use that as my default charge; that would stress me out, even if it's better for the battery. ;-)

Anyway, just my two cents. YMMV (!).

 

[brianman]

I don't need even 50% of the battery, daily

At the risk of bridging two topics...
If there was a supercharger within 25 miles of where I work OR we had a CHAdeMO adapter, I'd be tempted to set my charge point to 55% for a month to try it out.

 

[dsm363]

I agree. You paid for a car with over a two hundred mile range. Charging to 50% even though that's more than you need might leave you one day wishing you had charged the car more. I went to 80% for same reason.

 

[kendallpb]

At the risk of bridging two topics...
If there was a supercharger within 25 miles of where I work OR we had a CHAdeMO adapter, I'd be tempted to set my charge point to 55% for a month to try it out.

I can see the attraction, but it wouldn't really tempt me. One of the things I love is no refueling stops around town, ever! It's not a bit reason I bought the car--not really something I thought much about, honestly--but I do love it. The last time I let my other half drive the car without me, he was like "oh good, otherwise I would've had to get gas, 'cuz I'm running low." ;-)

 

[caddieo]

I have read in these forums that failure of the 12 volt battery gives more sudden and unforeseen problems than the foreseeable and therefore predictable exhaustion of the main battery. What is the effect on the 12 volt battery of maintaining a low SOC of the main battery - either by minimal charging or infrequent charging?

 

[brianman]

I can see the attraction, but it wouldn't really tempt me. One of the things I love is no refueling stops around town, ever! It's not a bit reason I bought the car--not really something I thought much about, honestly--but I do love it. The last time I let my other half drive the car without me, he was like "oh good, otherwise I would've had to get gas, 'cuz I'm running low." ;-)

If/when I go on a significant road-trip, I usually want to grab some mints and some water before the journey. I can easily burn 30 minutes doing that (if I try ) which is plenty of time for a 'lil CHAdeMO or SC love.

 

[Puyallup Bill]

Bear in mind that there will be degradation with age even if you never drive it, so you can't reduce degradation to zero. Also heat is a factor. So the worst conditions are hot and very high or very low SOC. I suspect but don't have any data to back this up, that even a small amount down from 100% gets a big reduction in degradation while from 90% to 70% only gets a moderate amount of reduction.

As a practical matter, what I would do, if I had 4.5 and was very concerned about battery life, would be to charge to the lowest SOC that gets me:

1. Three days plus 10% normal driving (In case of power outage or charging problems).

2. 90%.

3. So that after a day's driving SOC is not below 40% (low SOC is particularly bad if you also drive spiritedly).

But I doubt that there is all that much difference in battery life between doing that and just charging at 80% to 90% and not worrying about it.

The last sentence in the quote - BINGO! That is my position.

 

[stopcrazypp]

Here's two charts that can answer your question. Here's one direct from Panasonic for their NCA chemistry (figure 1):
http://ma.ecsdl.org/content/MA2011-02/17/1282.full.pdf

Keep in mind the degradation from storage is not linear (it goes with the square root of time) and that Tesla's BMS will attempt to maintain the temperature close to 25C, but anyways the capacity loss (in percentage) after 300 days of storage is:
30%SOC 25C: 1.8%
90%SOC 25C: 7.8%
30%SOC 60C: 12%
90%SOC 60C: 18.5%

Figure 1 in this NREL report also shows NCA degradation rates, but broken down into more SOC ranges. The graph is in in growth rate, but to be consistent I've computed the 300 day degradation at 25C, then the 8 year number too. There's no 90% number, but I extrapolated the rate data from the graph for a best guess. Again these numbers are the percentage (%) capacity loss:
20% SOC: 3.0, 9.3
40% SOC: 3.5, 10.9
60% SOC: 4.4, 13.6
80% SOC: 5.5, 17.2
90% SOC: 6.6, 20.6
100% SOC: 7.9, 24.8
http://www.nrel.gov/docs/fy12osti/53817.pdf

Most of the suggestion here make sense. The key thing is what matters is the amount of time you are in that high SOC, not the fact that you are in it. The goal is to minimize your average SOC. So you can charge to a high SOC as long as you don't remain in it for long periods of time.

 

[AmpedRealtor]

People can make this as complicated or easy as they want, it's their choice.

Charging only as much as we drive seems a little shortsighted, as the reason we bought a vehicle with 265-300 mile range is exactly so that we can take the occasional unplanned detour or road trip. Also, if you only charge as much as you drive, you can quickly find yourself stranded on the side of the road if you get caught in unexpected traffic. I'm sure we've all found ourselves in an unexpected freeway or lane closure more than a few times. Stop and go, bumper-to-bumper traffic takes a heavy toll on range.

Tesla's recommendations are easy and worry-free. Keep it charged to 90% so you are ready to go almost anywhere at any time. These are the people who designed this battery, they know what it can and cannot do. I mean no offense to anybody here and I am not singling anyone out, but I prefer to take my charging advice from Tesla over any number of people on the internet who I don't know and who also don't know any better than Tesla. My daily drive rarely exceeds 60-80 miles, but you can bet that I will keep my car charged to 90% just in case and to also have peace of mind.

- - - Updated - - -

Here's two charts that can answer your question. Here's one direct from Panasonic for their NCA chemistry (figure 1):
http://ma.ecsdl.org/content/MA2011-02/17/1282.full.pdf

Keep in mind the degradation from storage is not linear (it goes with the square root of time) and that Tesla's BMS will attempt to maintain the temperature close to 25C, but anyways the capacity loss after 300 days of storage is:
30%SOC 25C: 1.8
90%SOC 25C: 7.8
30%SOC 60C: 12
90%SOC 60C: 18.5

Figure 1 in this NREL report also shows NCA degradation rates, but broken down into more SOC ranges. The graph is in in growth rate, but to be consistent I've computed the 300 day degradation at 25C, then the 8 year number too. There's no 90% number, but I extrapolated the rate data from the graph for a best guess.
20%SOC: 1.6, 4.9
40%SOC: 2.2, 6.9
60%SOC: 3.3, 10.3
80%SOC: 4.7, 14.8
90%SOC: 6.8, 21.2
100%SOC: 7.8, 24.2

http://www.nrel.gov/docs/fy12osti/53817.pdf

Most of the suggestion here make sense. The key thing is what matters is the amount of time you are in that high SOC, not the fact that you are in it. The goal is to minimize your average SOC. So you can charge to a high SOC as long as you don't remain in it for long periods of time.

None of this is relevant, as Model S battery does not use the standard Panasonic chemistry. Tesla uses the Panasonic cell sizes, yes, but has customized almost everything else about these cells including the chemistry.

 

[stopcrazypp]

None of this is relevant, as Model S battery does not use the standard Panasonic chemistry. Tesla uses the Panasonic cell sizes, yes, but has customized almost everything else about these cells including the chemistry.

The OP asked for general battery degradation data. This is even better than general as it's the same NCA chemistry as the Model S is using. Yes the specific results will be different depending on the customizations Panasonic did, but you can get a pretty good picture of how degradation changes for various SOCs.

 

[WarpedOne]

My daily drive rarely exceeds 60-80 miles, but you can bet that I will keep my car charged to 90% just in case and to also have peace of mind.

Exactly.
It is still prudent to set the timer to start charging at particular time when those 80 miles of lost daily range will be recouped about an hour before your typical morning drive-off time.
In this simple and easy way you can more than halve the time the car sits at 90SOC, sacrifice no utility nor spend any extra energy/work. Let the technology take car of technology.

None of this is relevant, as Model S battery does not use the standard Panasonic chemistry. Tesla uses the Panasonic cell sizes, yes, but has customized almost everything else about these cells including the chemistry.

Just wrong.
Exact numbers to the last stated decimal place might be different, but general behavior is the same - high temperatures, higer SOC == faster degradation.

 

[markb1]

Given that they provide warranty for the battery, I'd be very surprised if there was a dramatic improvement in battery life by going down to 80%. If that was the case, Tesla would have a "storage mode" or something that keeps the car at a lower charge level.

But the warranty doesn't cover normal degradation of the battery.