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

[djp]

For my consideration (I need to stay above, say 80% capacity), it looks like I will greatly extend the life of my car by charging to a lower percentage (charging to 90% gives me ~7 years, whereas charging to 60% gives me longer than the probable life of the car (18 years).

True, but you'll also get degradation from charge cycles which isn't included on these graphs, so don't count on 18 years. If you're budgeting one replacement battery over the life of the car then running at a lower SOC isn't that important. I think Tesla is downplaying the degradation rates since 20% loss over 8 years is fine for most people.

For the Roadster the original guidance from Tesla was the batteries would lose 30% over 5 years and the actual numbers are coming in closer to 15-20% over 100,000 miles. But with replacement Roadster batteries costing $40K I'm trying to squeeze as much life out of mine as possible!

 

[stopcrazypp]

Unless my math is wrong, you are correct in that there are diminishing returns for degradation rate as SOC changes, and also diminishing returns in terms of "what % charge is left after X years". HOWEVER, since degradation (apparently) happens as a fractional (1/2) power with respect to time, if you look at "How many years till I only have X% battery charge left", there are no diminishing returns (in fact, the opposite).

My numbers were actually incorrect (I previously had them assuming the y-axis as 0 to -5, when the y-axis is -1 to -5; original post updated to fix). But what you observed is true (didn't actually notice that at first glance). I guess it depends on if you care more about how many years your battery will last or how many percentage your battery will be in x-amount of years.

 

[bob_p]

I was updated to the latest .61 release yesterday, and my charging screen is different. It doesn't make the comment about battery longevity.

 

[djp]

I was updated to the latest .61 release yesterday, and my charging screen is different. It doesn't make the comment about battery longevity.

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I think they've removed it to downplay the effects of SOC. It was probably confusing people to say that the battery life could be extended by trading off range. It's a simpler message to say charge to 90% and don't worry about it.

Losing 20% capacity over 7-8 years is good enough for most people since that's longer than they'll own the car.

 

[ElSupreme]

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 did this for a while. I am back to 90%.

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.

This is the reason why I charge to 90%. Every now and then I take a 180mile round trip. It is nice to easly do that and have some errand miles in the bag as well.

Remember that the charge percentage on the screen is NOT the charge percentage of the cells. Tesla is hiding the bottom and top of the cells from you. I would think 90% charge indent is close to 80% cell charge.

 

[qwk]

Remember that the charge percentage on the screen is NOT the charge percentage of the cells. Tesla is hiding the bottom and top of the cells from you. I would think 90% charge indent is close to 80% cell charge.

It's probably close. There is around 5% on either side hidden, so it's a wash.

 

[kendallpb]

Remember that the charge percentage on the screen is NOT the charge percentage of the cells. Tesla is hiding the bottom and top of the cells from you. I would think 90% charge indent is close to 80% cell charge.

I thought other sources also suggested 90% or lower, so I'm not sure this makes sense. We know they hide a little at the bottom (people run past "0"); they may hide a bit at the top, but probably not as much as at the bottom.

 

[Hengist]

The Model S lets you time charge, as in, start charging at this time. It doesn't let you time the end of the charge. ;-) Most people who're doing that, or all, are probably timing their start based on their average usage and how long that amount takes to charge. That's basically what I did. Although now I'm worried that by charging on these hot days, while the sun's out, I'm hurting my battery. Argh. ;-(

The Volt has the best charge timing that I have seen. You set up settings that describe both winter and summer times for off-peak, partial-peak, and peak electric rates. These can be set both for weekdays and weekends. and tou specify the rule for switching between winter and summer. And you set a time that you plan to leave each day.

The car figures out when to start charging based on all this info and on what power source it's plugged into. So it makes sure you're charging just in time and at the lowest cost.

You also get optional texts and emails when it's charged, if its not plugged in when it should be, and if the charge is interrupted.

Maybe we will get some of this in a future upgrade?