Question for the battery experts

[gcgp]

Would there be a difference in terms of battery longevity between the two scenarios?

1. Charge to 80% then drive and discharge to 60%, occasionally go down to 50%
2. Charge to 70% then drive and discharge to 50%, occasionally go down to 40%

This would be an almost daily (6 days a week, occasionally 7 days) cycle.

 

[LargeHamCollider]

2 will be better for a wide majority of chemistries, it's almost completely chemistry dependendent but my WAG would be 2 gets you a 10% cycle life increase over 1.

 

[houdini]

There's so many differing opinions on battery degradation - age, charge discharge. I am leaning towards age degradation rather than the others. There's Cabs in England that have done 100s thousands of miles and still show 100%. I lost a bar on my Leaf after 46,000kms and lots of DC fast charges, 100% charges etc. My Friend has a same age car, 3,000kms and lost a bar within a week of me.

 

[WarpedOne]

Would there be a difference in terms of battery longevity between the two scenarios?

1. Charge to 80% then drive and discharge to 60%, occasionally go down to 50%
2. Charge to 70% then drive and discharge to 50%, occasionally go down to 40%

This would be an almost daily (6 days a week, occasionally 7 days) cycle.

Yes, there would be a difference, but it is impossible to predict what exactly it would look like.

My recomendation is: charge to %80 and discharge down to %50, reducing the of number charging sessions by a third.

 

[paulp]

I doubt anyone on this forum has the knowledge to answer your question with complete certainty.

 

[scaesare]

As has been mentioned, there are likely many factors that will have greater impact than the relatively minor difference between those two charging regimes.

However, all else being equal, the general consensus for most Li-ion chemistries is that limiting excursions to the exterme on either end is preferable. A battery sitting at 50% charge is most likely to degrade the least.

Thus, your second senario centers your rannge of charges more in the "middle" of the battery range, and would probably be considered the slightly better option.

That having been said, it's also generally understood, that the degree of impact is non-linear and far greater at the very top and bottom ends (i.e. the impact to the battery is greater when going from 90% charge to 100% charge than from 70% to 80%).

Thus, I tend to bias my charging strategy to allow slightly more reserve range (typically 70-to-45% or so daily) to allow room on the bottom end in case of unexpected additional travel, higher energy use due to temps/weather, etc...

 

[Mark E]

I just set the daily charge limit at the Tesla recommendation of 90% and don't worry about it. With what we have seen from other cars by the time the battery actually needs to be replaced the upgrade options will most likely be much cheaper and probably larger capacity.

After nearly 30,000km and 20 months in the range has stabilised on my S85 at 347 typical km @90%. From memory when the car was new it might have been 349 or 350 perhaps, so not really an issue.

 

[gcgp]

Thanks for all the input guys. Mark E, your real-world numbers are very comforting. I expect I will be doing around 25-30,000 kms per year, maybe more. The most I did in a year was around 45,000 kms. My daily drives will only be between 50-100kms, Occasionally going to 120-150 maybe once a week. And that will only be just in the Gold Coast, does not include the occasional interstate trips. My 70D will be well used. I think I will call her "Nykola."

 

[paulp]

I just set the daily charge limit at the Tesla recommendation of 90% and don't worry about it. With what we have seen from other cars by the time the battery actually needs to be replaced the upgrade options will most likely be much cheaper and probably larger capacity.

After nearly 30,000km and 20 months in the range has stabilised on my S85 at 347 typical km @90%. From memory when the car was new it might have been 349 or 350 perhaps, so not really an issue.

Well thats very logical, treating your battery as recommended by Tesla.

 

[GSP]

...... I tend to bias my charging strategy to allow slightly more reserve range (typically 70-to-45% or so daily) to allow room on the bottom end in case of unexpected additional travel, higher energy use due to temps/weather, etc...

I recommend charging to 80% instead of 70% for the above reason. Anything below 90% will be good for battery life, and differences in life between 70-90% will be probably too small to measure.

It also is good to charge up to 100% occasionally, 4-6 times per year would be plenty. This helps SOC estimation and cell balancing. It is best for battery life to time the 100% charge to finish shortly before leaving (1-2 hours is fine), to minimize time spent at 95-100%.

GSP

 

[Brian May]

From the owners documentation (yes, I know reading the manual is weird thing that weirdos like myself do...):

Model S has one of the most sophisticated battery systems in the world. The most important way to preserve the Battery is to LEAVE YOUR Model S PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model S for several weeks. When plugged in, Model S wakes up when needed to automatically maintain a charge level that maximizes the lifetime of the Battery.

There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly.

Note: If the Model S Battery becomes completely discharged in a situation in which towing is required, the owner is responsible for towing expenses. Discharge-related towing expenses are not covered under the Roadside Assistance policy.

 

[Brian May]

The above documentation I quoted would seem to imply that the number of charging cycles isn't a significant factor for the overall life of the battery.

 

[alpal]

I think I will call her "Nykola."

Nice ...

 

[RichardMcN]

The above documentation I quoted would seem to imply that the number of charging cycles isn't a significant factor for the overall life of the battery.

Logical!

 

[championi]

Hey guys, I just noticed that my HPWC is charging about 10km/hr faster for no apparent reason. It used to charge at most 33km/hr, now it's doing 41km/hr? Could this possibly have something to do with the software update? By the way, it's always been on typical range and that hasn't changed

 

[championi]

Argh!! My bad. For some reason after the software update it changed from typical to rated range. Annoying!

 

[RichardMcN]

I just set the daily charge limit at the Tesla recommendation of 90% and don't worry about it.

Where is the 90% recommendation to be found? All I can find is this text (below) from the manual.

To adjust the charge limit, touch Set Charge Limit, then drag the slider bar. You can charge to any level from 50% to 100% based on your driving needs.

Is it hinting that if you don't drive much you should set it lower? Why have a 50% to 100% selectable charge limit if you are not expected to set it lower when you don't need as much?
.

 

[WhiteStar]

Where is the 90% recommendation to be found? All I can find is this text (below) from the manual.

Is it hinting that if you don't drive much you should set it lower? Why have a 50% to 100% selectable charge limit if you are not expected to set it lower when you don't need as much?
.

Exactly right. If you don’t need the daily range of 300 km, why keep it charged at 80%? Cells are happier & less stressed at 50 or 60%. I think Tesla’s manual has changed to reflect this without being too specific. Whatever might have been stated previously regarding higher state of charge levels could possibly be for purposes of expediency. If Tesla said unambiguously to stay at 50 or 60% SOC unless higher range is required, naysayers would jump on it and say battery degradation is a huge issue…which it is not.

 

[TesAus]

Exactly right. If you don’t need the daily range of 300 km, why keep it charged at 80%? Cells are happier & less stressed at 50 or 60%. I think Tesla’s manual has changed to reflect this without being too specific. Whatever might have been stated previously regarding higher state of charge levels could possibly be for purposes of expediency. If Tesla said unambiguously to stay at 50 or 60% SOC unless higher range is required, naysayers would jump on it and say battery degradation is a huge issue…which it is not.

Also in early days before people get used to planning ahead they are more likely to get caught short with starting each day with only 50%?

 

[WhiteStar]

Also in early days before people get used to planning ahead they are more likely to get caught short with starting each day with only 50%?

That makes sense. With the proliferation of Superchargers there’s even less reason for consistent higher charge levels although as others have said, it’s a good idea to go to higher levels (from what I've read, maybe 95% or more at least every couple of months) so that cell balancing is performed at regular intervals.