How much better is 80% instead of 90% for the battery?

[hingisfan]

Maybe I'll try a compromise....
1. Charge to 85%
2. Delay charge start time till 11pm (was 7pm). I'm too worried about loss of household power overnight to cut it closer on the start time.
3. Set current to 35 amps... I've been doing this already for a while. I figure it will be a bit easier on my UMC instead of running it full out at 40 all the time.

 

[AmpedRealtor]

The way I work the excessive heat is...

Why would you need to consciously do anything to mitigate battery heat when the car has one of the most advanced battery management systems on earth that automatically ensures the battery temperature does not get out of line?

 

[apacheguy]

Why would you need to consciously do anything to mitigate battery heat when the car has one of the most advanced battery management systems on earth that automatically ensures the battery temperature does not get out of line?

That's true, but when the car is off and the contactors are open there is no thermal management going on. Some of us worry about the cells idling in heat.

Often times when I return to my car on a hot day, it aggressively begins to chill the battery (as evidenced by side louvers opening and fans spinning up to max) indicating the temps got out of line.

 

[andrewket]

I installed a in-window air conditioner in my garage to keep the temps down in the summer because of our EVs (the energy consumed for these high efficiency units is small.) Unfortunately my HOA had other ideas and I had to remove it

 

[LetsGoFast]

That's true, but when the car is off and the contactors are open there is no thermal management going on. Some of us worry about the cells idling in heat.

My car runs the AC and leaves a puddle in my garage fairly often. Maybe it only does that when it is charging?

 

[jerry33]

Why would you need to consciously do anything to mitigate battery heat when the car has one of the most advanced battery management systems on earth that automatically ensures the battery temperature does not get out of line?

My understanding is that the higher the temperature and the higher the SOC, the shorter the battery life. And as Apacheguy says, when the contactors are open there is no thermal management, and the car typically sits for far more hours a day than it runs or charges. Also from the posts, it appears that the Model S isn't as aggressive in temperature management as the Roadster. So the plan is to keep the SOC relatively low for a relatively long period of time. (Relatively low means that I have enough range for three commutes after charging finishes.)

- - - Updated - - -

My car runs the AC and leaves a puddle in my garage fairly often. Maybe it only does that when it is charging?

If plugged in, it should do it whenever the temperature reaches some set point, but I think that will only happen on the wakeup schedule when it checks the 12V battery (or at any other time the car is awake).

 

[apacheguy]

If plugged in, it should do it whenever the temperature reaches some set point, but I think that will only happen on the wakeup schedule when it checks the 12V battery (or at any other time the car is awake).

Right, seems to only happen when the car wakes up to maintain the 12 V. Or during charging. Or when the car is on. Outside of that, all my data indicates that it does not maintain a temp set point.

If mine is going to sit in heat all day I generally plan to keep it less than 70%.

 

[wk057]

I charge to 90% daily and don't even bother thinking about it anymore. For trips I charge to 100%, and the only thing I do is try to minimize the amount of time the pack sits at 100%.

This ^

The pack voltage difference at 90% vs 80% is not significant. Literally about 10V at the pack level, which is 0.1V difference at the cell level. The jump from 90 to 100% is 50% more voltage change (~0.15V per cell).

In any case, the difference between sitting at 4.05V and 3.95V per cell is not going change much since the cells are not fully charged in either case. Sitting at 100% or < 10% for a significant amount of time without discharging or charging, respectively, very soon after reaching that point is what hurts the cells. Leaving them at lower charges for longer is, from my understanding, worse than higher charges. Depending on the temperature of the cells things can get much worse or slightly better from a degradation standpoint.

Long story short, I charge to 90% normally, and 100% whenever I need the extra range. I don't leave the car at 100% for more than a few minutes before driving, normally, and I don't leave the car < ~20% without charging at my destination (supercharger or home, usually). I'm pretty sure this basic practice will save me from significant degradation.

So far I've not lost 1 mile on the P85D after 14,000 miles and have lost 1 mile on the P85 after about the same 14,000 miles.