What should my ideal charge percentage be?

[lolachampcar]

I find the comment about rated range an interesting one. The very first experience I had with my 2012 Zero DS was that I did not make anywhere near the advertised range at highway speeds as I was trying to get back home from picking the bike up. No emergency as I just had my buddy go a ten miles further down the turnpike to get me but my very first impression of the company was that they lied to me about range.

Fast forward to MS and I go for a 170 mile trip from my house to the South Beach Tesla store, have lunch and return while making rated range the whole time. Most of the miles were in a pack going down I-95 at 70 mph with the ac on with the remainder in stop and go South Beach traffic. I was pleased. Tesla told me the truth.

 

[Al Sherman]

Does anyone actually get EPA rated miles?

I do quite frequently but am driving pretty slowly (30-40) on 2 lane county roads for the most part. My suspicion is that with everything else being equal (temp, gradients, heat use etc...) it is pretty hard to get rated without driving slowly. I drive the speed limit when on interstates and am close to rated but usually don't quite get there.

 

[strider]

The cooling system in the Roadster kicks in above 105F.

I don't think this is quite correct. If you are running the A/C, the car seems to divert some of it to the battery even if it's at nominal temp. Here's why I think this...

Last week temps were in the mid 70's. One day I drove home with the top on and A/C running. When I got home and plugged in the Tattler reported battery temp as 26C. The next day I drove home with the roof off and no HVAC and when I got home the Tattler reported a battery temp of 31C. Same commute, same ambient temp.

The car also makes decision based on what the ambient temp sensor is seeing and will increase or decrease charging cycles accordingly.

But you are right in that the car deems 40C (104F) as a threshold for battery life and will try very hard to keep it below this temp.

 

[rlang59]

I think of this like the sunroof. I like the idea of "set it where you like, with high granularity" but adding notches for "typical settings" like the Pano would alleviate the "choices overload" part of the experience for some users.

Don't have the sunroof never use them. But I still think this adds an unnecessary layer of complexity as can be seen by comments from people like gaswalla. They should have left it alone and added an advanced menu for those who wanted it.

 

[NigelM]

Mod Note: This thread was carved out of the Firmware v4.5 thread for further discussion on what the ideal battery percentage should be. User Interface discussions should please continue in the original thread.

(Also made this thread 'sticky' for now)

 

[kendallpb]

I'm not worried about bricking or zero charge. But using the bottom 10-15% of the battery is pretty hard on it, even more than using the top 10-15% of the battery capacity. And the poster to whom we were responding is using a charging setpoint of 50% for battery longevity... but if the goal is to take care of the battery's health in the best possible way and you're only going to use 30% of the range on a daily basis, charging to 50 and using the 20-50% range is not as good for the battery's lifespan as charging to 65 and then using the 35-65 range of the battery.

(shaking head) And some people thought I was silly for saying Tesla has complicated EVs.... ;-) Sigh. I'll set it to a random % every day and see what happens.

- - - Updated - - -

That's not what the data from the US Army study shows. They saw better battery life cycling between 0% and 50% than cycling between 25% and 75%.

No question you should charge higher if you need the range or want a buffer for unplanned trips, but in terms of battery life the lower the average SOC the better.

People keep mentioning this study, but even if the battery chemistry's the same, if they weren't testing Tesla cars, is this 100% directly applicable? Tesla has a sophisticated battery management system--does this not enter into the picture at all? Just wondering--not a battery person.

 

[brianman]

He said "exceeds mileage" which I interpreted to mean if the EPA on a car is 25 MPG and I actually get 27 MPG then I have "exceeded" the EPA rating because I'm getting "more" distance per unit of fuel... but I see what you mean :smile:

His post was mileage, yours was "mileage inverted" right? Hence my point that it's quickly confusing.

mileage

I exceed EPA rated mileage nearly every day

1/mileage

I easily get 300 Wh/mi or less.

- - - Updated - - -

But I still think this adds an unnecessary layer of complexity as can be seen by comments from people like gaswalla. They should have left it alone and added an advanced menu for those who wanted it.

They should make a "simple" button so you can get back your "limited options" UI. :wink:

 

[djp]

People keep mentioning this study, but even if the battery chemistry's the same, if they weren't testing Tesla cars, is this 100% directly applicable? Tesla has a sophisticated battery management system--does this not enter into the picture at all? Just wondering--not a battery person.

The US Army study is on the Roadster chemistry (LiCoO2) and the NREL study is on the Model S chemistry (NCA). Both studies have similar results, and Tesla battery management is similar for both the Roadster and Model S, so the general principles can be applied to both.

The Battery Management System tries to keep the battery above freezing and below 104F. The US Army study has three runs, one at 32F, one at 68F and one at 104F, so it's an excellent match for the BMS range and can be used to bracket what we'd expect to see in the real world.

The overall conclusion is that low temperatures and low SOC help extend battery life, and high temperatures and high SOC reduce battery life. Both in combination are especially bad. A low SOC can help protect against high temperatures and low temperatures can protect against a high SOC.

Even Elon said the batteries should last forever in Alaska. If you're in a warmer State (or have a hot summer) then lowering the SOC will help protect the battery.

Personally I don't think this is too complex for the average person, but will take some education. I think it's mostly about managing expectations for potential buyers.

When I bought my Roadster I expected the battery capacity would drop to 70-80% over 8 years. If I run at 90% Standard Charge in a warm climate that's probably true. Now that I know I can get better numbers by dropping the SOC I'm a very happy camper, especially since I don't need the full Standard range on a daily basis. So far I've seen no degradation after three years by running at 50%.

 

[Al Sherman]

Now that I know I can get better numbers by dropping the SOC I'm a very happy camper, especially since I don't need the full Standard range on a daily basis. So far I've seen no degradation after three years by running at 50%.

Yes. I'm happy to have the slider. I rarely use 15% of the P85 capacity. I think djp's lack of degradation in conjunction with the studies cited is significant. Yes it's a drop in the bucket, but I'd like to keep my battery from being recycled that much longer. Certainly not applicable to everyone but it works for me.

I would STILL like to see a number from Tesla engineers for folks (like me) who rarely (if ever) need more than a small percentage of available range.

 

[steve841]

So far I've seen no degradation after three years by running at 50%.

No disrespect but....If you never charge above 50% .... how do you know your battery has not degraded?

 

[andrewket]

If you never charge above 50% .... how do you know your battery has not degraded?

Funny, I had the same thought. Occasional range charge, I guess.

 

[djp]

No disrespect but....If you never charge above 50% .... how do you know your battery has not degraded?

I still do Standard charges once or twice a month and Range charges a few times a year. My last Range charge four weeks ago was 394km, identical to when I first bought the car.

 

[dsm363]

life was easier with the standard vs range choice

You can still set the charge to 90% (standard was 92%) and leave it. Not too complicated.

People asked for this feature so Tesla provided it. Now people say it is too complex.

 

[ElSupreme]

People asked for this feature so Tesla provided it. Now people say it is too complex.

In general people always want tons of options, and say they want the ability to customize their stuff. But in actuality most people don't actually want it.\

Apple has generally made decisions for people. And restricted choice, and given a generally very well received product.

In fact there is a RadioLab about choice that brings up the fact that more than 7 choices and things start falling apart.
http://www.radiolab.org/2008/nov/17/

 

[dtich]

Well, after all the discussion about maximizing battery life in normal operation and the new 4.5 release, I wanted to point out that the battery charge level control is awesome for VACATION mode or extended storage of any kind. Any battery life improvements likely in normal day-to-day operations (where the car is discharged part of the day) will be multiplied in a storage scenario. It's best to keep a stored battery on the charger, but it's also best to maintain a lower SOC -- this update accomplishes that perfectly in a way that was relatively hard to achieve before now.

Freekin' YAY.

exactly. this is why i've been anxious for it. i routinely go out of town for days to weeks. this is a BOON. glad to have it.

given my driving needs i will probably set to 80 or 85 as a normal setting, getting me around, eh, 225 miles rated. fine. never usually get close to that but it's there if i need it and i don't want to be caught up in setting a custom charge level every night - if others here would also commit to this thinking i think the slider usage would be non-anxiety producing. just decide OVERALL how you need to use it, and then do that. if you want to keep it at 93% (as my current standard charge seems to be), then just do that. problem solved.

but now that i have it, setting it to 50 or 60 when i leave town is fabuloso. i do not intend to replace this car in 4 years. maybe 8. (unless the mark 2 is just to die for... not even gonna go there.) so battery longevity is worth a moments' thought here and there to me for sure.

that said, i DO think an 'expert' mode where this slider is used and a 'normal' mode where it just allows standard and range, is probably a good idea. although MOST seem to be, not all model s owners are geeks who stay up at night trying to save 2 or 3% battery capacity over the next four years. only some of us. for the rest, sure why not, make it real easy. where's the harm in that.

but i likey the percentage slider. very useful in my particular case.


merci.

 

[brianman]

People asked for this feature so Tesla provided it. Now people say it is too complex.

In general people always want tons of options, and say they want the ability to customize their stuff. But in actuality most people don't actually want it.

One of the dangers of generalizing.

Jim: My favorite color is blue.
Joe: My favorite color is blue.
Jane: My favorite color is pink.

Conclusions:
1. Jim and Joe must be somehow different from Jane.
2. All people with 3 letter names prefer blue.
3. All people with 4 letter names prefer pink.
4. No people prefer any color other than blue or pink.


On a somewhat related note...
"I think they should remove the Creep feature because I like the original default of Off and it confuses me to see options displayed that I don't use."

I think most would agree this is patently absurd. I feel similarly about "they should remove a feature that people have asked for because other people find it potentially confusing."

 

[bollar]

What should my ideal charge %age be? (FWv4.5)

Not that this will sway anyone who's really into this thread, but...

And yes, I got bitten by autocorrect. I'm pretty sure I know the difference between since and sense.

 

[dtich]

oh this is interesting too, i didn't consider that setting the charging slider to a lower/lowish percentage could inhibit regen performance as it would be possible to more easily exceed the recharge level with regen. right?

not that it matters much to me, i can't see a scenario where i'm out driving and get close enough to my charge level to inhibit braking regen. i suppose if you charged to 80, then set it 50 and started driving that might turn regen off for a while, no? not sure how it works...

 

[dsm363]

I started charging at 80% so close to 200 rated miles. More than I'll ever need in a normal day. Will have to check the regen again to see if it feels different.

This is only a feature that I think people who experienced the car with standard/range charge will possibly miss but they'll get used to the new way quickly. It's not complicated. People who come to the car having never seen the old way will adjust more easily.

 

[djp]

oh this is interesting too, i didn't consider that setting the charging slider to a lower/lowish percentage could inhibit regen performance as it would be possible to more easily exceed the recharge level with regen. right?

not that it matters much to me, i can't see a scenario where i'm out driving and get close enough to my charge level to inhibit braking regen. i suppose if you charged to 80, then set it 50 and started driving that might turn regen off for a while, no? not sure how it works...

Elon's referring to regen being disabled or reduced when charging above 95%. There's no difference in regen at lower charge levels.