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What should my ideal charge percentage be?

djp

Model 3 Performance
Aug 28, 2011
1,120
59
Toronto, Canada
To provide some closure to this thread, the ideal setting to extend battery life is to charge to less than 75% SOC.

Why do Li-ion Batteries die? And how to improve the situation?

Here is the response:

"Thanks for this e-mail. I have placed responses within your text using CAPS (not yelling) but so you can find my responses


Jeff Dahn, FRSC
Professor of Physics and Atmospheric Science
NSERC/3M Canada Industrial Research Chair
Canada Research Chair"

"Since electricity appears to have become the defacto currency for renewable energy and I have a great interest in and now investment in renewable technologies (own a Nissan Leaf and Tesla Model S and a 9.8 kW PV system), I have been doing my best to learn whatever I can about energy storage and how batteries work, in particular, the way end user habits effect overall life.

THIS IS AWESOME.

I am wondering if your research has revealed what the best way to extend a batteries life is. I have concluded, as you have noted, that high ambient temperatures degrade these batteries the most. Living in Seattle, we are blessed with a moderate climate so I feel pretty fortunate in that regard.

ABSOLUTELY. AVOID HIGH T WHENEVER POSSIBLE.

Debate continues on whether charging habits will turn out to have much effect on battery life. I have started leaving all of my li-ion consumer products at about 50% charge when they are not in use. Tesla makes this very easy with a battery slider that allows the consumer to choose between 50% and 100% end charging and even has this feature integrated into the phone app to make it very easy to adjust upwards on the fly as long as the car is plugged in. I have installed an 80A (20 kWh) charger so that I can quickly add charge to the Tesla S, allowing me to minimize the inconveniences associated with leaving the pack at a low state of charge and thus increasing the amount of time the battery stays at a mid/low SOC. I tend to do mid pack cycling, discharging generally between 30 and 70% when convenient, while aiming to have the car sit for the longer stretches like overnight, at 50%. I'm not religious about this, just tend to aim in this direction generally.

I THINK THAT IF YOU ARE KEEPING THE CELLS BELOW 4.0V (NO WAY FOR YOU TO TELL THAT, HOWEVER) THE BATTERY LIFE WILL BE VERY IMPRESSIVE. WE ARE TESTING CELLS BUILT IN 2002 THAT HAVE 2002 TECHNOLOGY (LIFETIME IS BETTER NOW) THAT STILL HAVE 75% OF THEIR INITIAL CAPACITY (CYLCED AT 37c THE WHOLE TIME). THESE CELLS WERE CHARGED ONLY TO 4.075V. MODERN CELLS LIKE THOSE IN TESLA CHARGED TO 4.0V SHOULD LAST A FEW DECADES, I SUSPECT, WITHOUT ANY ISSUE (SO KEEP YOUR CAR FROM RUSTING!). WHERE IS 4.0V RELATIVE TO STATE OF CHARGE? MAYBE 75%.

ONE OTHER THING I WOULD RECOMMEND IS TO AVOID HIGH RATE CHARGING AT TEMPERATURE BELOW 0C. ESPECIALLY WHEN THE CELLS ARE ABOVE 75% SOC. TESLA ELECTRONICS MAY PREVENT THIS

In your opinion, do you believe it is worth the effort to keep li-ion batteries at 50% or thereabouts for the bulk of their resting time to extend their long term capacity and if so, do you have any idea how much of a difference this is likely to make over say a 8-15 year time period.

KEEPING BELOW 4.0V MAY DOUBLE OR TRIPLE LIFE TIME COMPARED TO A FULL CHARGE EVERY CYCLE, I SUSPECT.

Also, given that Tesla limits power to the motor during extremes, like high and low charge and high and low temperatures, is there really any reason to avoid running the battery low, assuming Tesla doesn't let you discharge the battery all the way anyway and limits discharge rate as the charge level drops. I assume running the battery to zero (of what the manufacturer allows) does little to the overall life as long as it gets recharged soon after. I assume that low and high states of charge are more an issue if exposure is prolonged, is that correct?

I THINK THAT REALLY DEEP DISCHARGE SHOULD BE AVOIDED AS THEN THE GRAPHITE EMPTIES OF LI AND THE CELL POTENTIAL RISES TO THE POINT WEHRE THE SEI ON THE GRAPHITE SIDE CAN BE DAMAGED. KEEP THE CELLS ABOVE 3.0V PER CELL (NO WAY YOU CAN TELL THAT) BUT THAT WOULD BE ABOUT 98% DISCHARGED. SO DO NOT DISCHARGE BEYOND 98%.

Any opinion you may have on this subject will be much appreciated in helping me understand what the limits of this technology are and how to best treat the batteries in my cars and consumer products.

THE TECHNOLOGY IS REALLY PRETTY AMAZING WHEN YOU THINK OF IT. "
 

JoeNe

EU P 1662
Dec 24, 2012
1,620
123
Wijgmaal, Belgium, Europe
  • Like
Reactions: Vern Padgett

djp

Model 3 Performance
Aug 28, 2011
1,120
59
Toronto, Canada
What should my ideal charge percentage be? (FWv4.5)

That's a nice summary. Thanks for that. If I understand correctly with 75% we stay below 4.0V?

On the Roadster 75% is roughly 4.0V. The Model S uses a newer chemistry but the voltages are probably in the same ballpark. Professor Dahn also thinks 4.0V is about 75% on the Model S, and described the 80% max on the Chevy Volt as being decent.

Based on his research, the best charging strategy to extend your battery's life is to charge under 75% on a daily basis, and top up higher when you need to take a longer trip.
 

donv

Member
Jul 15, 2013
599
47
Lake Jeanclia, OR
There is a guy in another thread (in "Driving Dynamics") with 40k miles on his Model S, who range charges (100%) EVERY DAY and has seen no degradation. In fact, still gets 264 miles of rated range. How does that square with the 70% thing?
 
  • Informative
Reactions: Vern Padgett

hans

P631
Sep 27, 2012
1,132
13
Menlo Park
There is a guy in another thread (in "Driving Dynamics") with 40k miles on his Model S, who range charges (100%) EVERY DAY and has seen no degradation. In fact, still gets 264 miles of rated range. How does that square with the 70% thing?

He only started charging to 100% in the past few months (in order to rebalanced the pack) so this case is not inconsistent with the general wisdom on degradation.
 
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Reactions: Vern Padgett

pilotSteve

Active Member
Jul 14, 2012
1,473
1,337
Prescott Az
That's a nice summary. Thanks for that. If I understand correctly with 75% we stay below 4.0V?

The other factor is heath. But that's managed by Tesla's Battery management.
Good tip, I enjoyed watching the video.

New twist to this thread: how fast should you charge, e.g. At what kWh? I got the idea from that video that three major factors affect Li cell life: (1) voltage cell charges to (2) temperature and (3) total TIME spent charging.

As long as Tesla is managing 1 and 2 plus we can actively manage 1 by choosing to charge to a lower percent capacity, then should we also consider charging at 10kWh (single charger) or perhaps 20kWh (twin chargers and HPWC AC) rather then 'dialing back' to reduce total time spent charging?

This may also give clues why supercharging is not limited by Tesla.
 

Jolinar

Member
Dec 20, 2012
15
0
EU
... then should we also consider charging at 10kWh (single charger) or perhaps 20kWh (twin chargers and HPWC AC) ...

First of all, it's kW not kWh...
  • kW means power you are pushing to the battery or power geting out of the battery.
  • kWh means total energ stored in the battery.
  • C means kW/kWh. So constant 1C would charge your battery in 1 hour. 2C in 30 minutes and 0.5C in 2 hours.

Second: kW is not that important as C rate. Higher C rate has higher damaging factor to the battery, that's why old Model Ses can SuperCharge at 90kW (1.05C for 85kWh) while newer Mode Ses with newer battery can charge at 120kW (1.41C for 85kWh)
 

pilotSteve

Active Member
Jul 14, 2012
1,473
1,337
Prescott Az
First of all, it's kW not kWh...
  • kW means power you are pushing to the battery or power geting out of the battery.
  • kWh means total energ stored in the battery.
  • C means kW/kWh. So constant 1C would charge your battery in 1 hour. 2C in 30 minutes and 0.5C in 2 hours.

Second: kW is not that important as C rate. Higher C rate has higher damaging factor to the battery, that's why old Model Ses can SuperCharge at 90kW (1.05C for 85kWh) while newer Mode Ses with newer battery can charge at 120kW (1.41C for 85kWh)

Yes, typo my bad. So what did you take from his graph showing (I thought) total charge time was also a key factor in life degradation? Hence my q about merits of higher current charging for shorter time?
 

Username

Member
Feb 27, 2014
113
2
Toronto
Unfortunately, 50% of range per charge works out to about 120 km or 80 miles of real mileage which is unacceptable.
Perhaps the thing to do since the battery is warranted for 8 years unlimited mileage is to charge the crap out of it at 100% everyday and it will die within the 8 year warranty period.
Tesla will then give you a free battery. No range anxiety with this method.
 
May 13, 2011
273
35
Palm springs, California
I drive ten miles per day, so I only charge to fifty miles...just in case. My total capacity has not changed, and remains at 268 miles. I have only taken three roads trips, but that is about to change. S, best car ever!!! Look for my national road trip tour, which will have daily posts on twitter. Go Tesla!
:)
 

dirkhh

Middle-aged Member
Jul 7, 2013
3,638
126
Portland, OR, USA
Higher C rate has higher damaging factor to the battery, that's why old Model Ses can SuperCharge at 90kW (1.05C for 85kWh) while newer Mode Ses with newer battery can charge at 120kW (1.41C for 85kWh)
And the 60kWh battery is charged with up to 1.7C (102kWh). Maybe that's part of the reason why they aren't giving an unlimited warranty on the 60...
 

nlc

Member
Jul 1, 2013
657
25
Nantes, France
Personally, I charge everyday my S85 to 70%, and I try to calculate the charging startup hour to finish the charge just before I go to work.
When at work I am between 50 and 60% SoC, thus it's the ideal SoC for long term storage.
And when at home the evening, the SoC is approx 30%, waiting for the charge startup :smile:
 

EchoDelta

Supporting Member
Mar 5, 2012
1,220
618
RootedNW.org, Seattle, Planet Earth
The problem with recommending a "best" number is there is no one best number for everyone, only what's best for you based on how you drive your car.

Well , my conclusion is the opposite.
nobody but tesla knows better what the battery use and charge patterns, ambient temperatures, seasonality, weekly cycles, Etc are **for your car**. that's exactly why they should have a suggestion

(albeit very discrete, like an opt-in marker on the bar that you can make show up after "agreeing" that suggestion just is based on the average past and doesn't know about your plans later in the day)

They could even be playing with this based on collected data internally and calibrating margins to reduce non-extreme outliers

Maybe in the future cars will have 3 charging options- typical, 90%, and range; if there's a business pressure to reduce battery decay without having to know too much.
 

dirkhh

Middle-aged Member
Jul 7, 2013
3,638
126
Portland, OR, USA
Well , my conclusion is the opposite.
nobody but tesla knows better what the battery use and charge patterns, ambient temperatures, seasonality, weekly cycles, Etc are **for your car**. that's exactly why they should have a suggestion

(albeit very discrete, like an opt-in marker on the bar that you can make show up after "agreeing" that suggestion just is based on the average past and doesn't know about your plans later in the day)

They could even be playing with this based on collected data internally and calibrating margins to reduce non-extreme outliers

Maybe in the future cars will have 3 charging options- typical, 90%, and range; if there's a business pressure to reduce battery decay without having to know too much.

This is what I'm hoping for after the 6.0 update of the nav system. I can tell the car "tomorrow is the usual" or "tomorrow I'll drive to xyz" and it picks the best charge rate...

OK, I guess this will be in the 8.7 firmware update :p
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Mar 8, 2012
19,632
22,279
Texas
Maybe in the future cars will have 3 charging options- typical, 90%, and range; if there's a business pressure to reduce battery decay without having to know too much.

That will only happen if the EPA changes the way range is calculated. Right now if you have discrete selections, range is based on an average of the selections (e.g. lower).
 

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