What should my ideal charge percentage be?

[David99]

I recall that there was some evidence or theory that it was harmful to the battery to run so low. I thought being in the single digits was worse for the battery than being in the 90s. But afraid I can't recall the source of this.

I go by what Jeff Dahn said who is working closely with Tesla on battery technology.

I quote him
"- Discharging to 5% state of charge (95% discharge) doesn't harm the battery either. Discharging all the way, which could be damaging, is actually prevented by the Tesla pack control electronics."

Here is the source:
Charging for optimum battery life | Tesla

So yes, it is perfectly fine to discharge your car to near zero in terms of battery health. I would highly recommend not aiming for lower than 10% for many reasons. But when it comes strictly to battery health and longevity, it is perfectly fine to go low.

 

[David99]

This may or may not be relevant for Teslas... but I currently have a 2014 Nissan Leaf that I have charged to 100% pretty much *everyday* as a daily commuter. The charging timer is set to finish charging to 100% at 7am and I typically drive to work around 9-9:30 am and I come back home with about 40-50% charge remaining. After 45k miles, and 3 years and 3 months, there is *no* battery level drop. Nissan Leafs have 12 battery capacity bars and I still have all 12 bars on the dash. I don't have any other way to validate the capacity, but thought to share these stats.

Edit: About a dozen times during my ownership, I have also driven the car to almost empty.

That's awesome to hear. The Leaf got a bad reputation for quickly degrading batteries. Looks like they got that fixed!

 

[ishareit]

This may or may not be relevant for Teslas... but I currently have a 2014 Nissan Leaf that I have charged to 100% pretty much *everyday* as a daily commuter. The charging timer is set to finish charging to 100% at 7am and I typically drive to work around 9-9:30 am and I come back home with about 40-50% charge remaining. After 45k miles, and 3 years and 3 months, there is *no* battery level drop. Nissan Leafs have 12 battery capacity bars and I still have all 12 bars on the dash. I don't have any other way to validate the capacity, but thought to share these stats.

Edit: About a dozen times during my ownership, I have also driven the car to almost empty.

Lol. I just came back from a trip to the hardware store and lost one bar. What a coincidence! Still more than 90% remaining with always charging to 100% for the last 3.3 years and zero thoughts given to maximizing battery life.

 

[bhzmark]

Sayeth Martin Eberhard: "Avoiding very high and very low states of charge. Voltages over 4.15V/cell (about 95 percent state of charge [SOC]) and voltages below 3.00V/cell (about 2 percent SOC) cause more stress on the insides of the cell (both physical and electrical)."


A Bit About Batteries

Maybe the BMS prevents it from ever getting that low? I dunno. I hope so. Rather not find out and so keep it charged at 90 to reduce risk of ever finding out.

I go by what Jeff Dahn said who is working closely with Tesla on battery technology.

I quote him
"- Discharging to 5% state of charge (95% discharge) doesn't harm the battery either. Discharging all the way, which could be damaging, is actually prevented by the Tesla pack control electronics."

Here is the source:
Charging for optimum battery life | Tesla

So yes, it is perfectly fine to discharge your car to near zero in terms of battery health. I would highly recommend not aiming for lower than 10% for many reasons. But when it comes strictly to battery health and longevity, it is perfectly fine to go low.

 

[Viking1]

I try to keep the car charged to 90% all the time -- just in case. Lots of evidence that a regular 90% charge doesn't cause any significant degradation over long times.

May I ask your mileage and degradation?

From personal experience I do agree with keeping the battery charged. I've asked a few people in a different thread (What is your 90%), when they say they have had little degradation, what has been their depth of discharge. They said their depth of discharge was shallow and they keep their batteries pretty well topped off (90%).

 

[12Pack]

Should also keep in my mind that battery "calendar life" is affected by SOC over the battery lifetime. From the above Tesla blog post:
"Two factors shorten calendar life considerably: lifetime average temperature and time spent at high states of charge. Batteries would last the longest if they were stored in a refrigerator at a very low state of charge" (my emphasis).

Keeping that in mind, I am charging to 60% routinely (do less than 20 miles/day usually) - while allowing for a full charge ahead of a long trip.

 

[Rodolfo Paiz]

For whatever it's worth, I sold a four-year-old Model S with about 25,000 miles on it, and had 98% of my original battery capacity. Air-conditioned garage, and charged to 70% on a daily basis, full charge whenever necessary or about every 8 weeks just because. From what I've read, lithium-ion batteries are happiest when not staying near full or near empty for a long time.

 

[Veritas1980]

For whatever it's worth, I sold a four-year-old Model S with about 25,000 miles on it, and had 98% of my original battery capacity. Air-conditioned garage, and charged to 70% on a daily basis, full charge whenever necessary or about every 8 weeks just because. From what I've read, lithium-ion batteries are happiest when not staying near full or near empty for a long time.

Those are some very nice numbers. I’m running something similar with mine, so can I ask how much of the 70% you would use on your daily commute?

 

[Rodolfo Paiz]

Not much. Once or twice a week, about 60 miles. The rest of the week, maybe 20 miles a day. I work from home a couple of days a week so I can concentrate better on certain tasks, so on some days I don't even leave the house. I think my lowest battery charge level ever was around 10%, just once or twice... otherwise I never drained the battery below 25% in my usage.

 

[Big Earl]

Lol. I just came back from a trip to the hardware store and lost one bar. What a coincidence! Still more than 90% remaining with always charging to 100% for the last 3.3 years and zero thoughts given to maximizing battery life.

I believe the first health segment disappears at 85% SOH on pre-2016 (?) LEAFs (first segment represents 15%, each subsequent segment represents 7.5%). Newer cars have made that first segment even wider - I've heard numbers from 78-80% SOH before the first segment disappears on 2016s and 2017s.

Either way, Nissan has a battery longevity problem due to the combination of no thermal management and poor chemistry choices. Many LEAF owners are reporting problems even with the upgraded "Lizard" packs.

My 2013 Fiat 500e does not have an option for charge level - it always charges to 100%. I hope that Fiat's chemistry and active thermal management are able to minimize degradation even though it gets charged to 100% nearly every night.

Now back to your regularly scheduled programming...

 

[alehbaba]

I also thought someone also recently reported running out when he still had a a few percentage showing.

For these reasons I'm inclined to minimize the chance that I might have to run the battery deep into the single digits and also being caught having to make a long trip without a SC en route and not having sufficient charge.

This actually happened once when I had to take a pet to a 24 hour vet hospital that was far away, late at night and no SC en route. Luckily I had charged to 90% right away earlier that night -- rather than charging to only 70 or 80% or delaying the charge start until 2am. I try to keep the car charged to 90% all the time -- just in case. Lots of evidence that a regular 90% charge doesn't cause any significant degradation over long times.

yes this is the case alot. Never know when you will have to go somewhere farther away after you only charged to 70-80% one day.It does happen. But daily is usually under 100 miles so 70-80% is fine and plug in every nite with charging starting at 3am.

 

[alehbaba]

Tesla battery expert recommends daily charging limit to optimize durability

Jeff Dahn, a renowned battery researcher and the leader of Tesla’s research partnership through his battery-research group at Dalhousie University, has been working on li-ion battery durability for Tesla for a year now.

One of those things is not charging to a full charge too often. Repeated full charges can arm li-ion battery cells, which is why Tesla recommends to only daily charge to 90% capacity and to charge to 100% only when needed for long trips. In the past, CEO Elon Musk even recommended 80% daily charging:

View attachment 245176

A Model X owner on TMC aims to keep his all-electric SUV for up to 20 years and he decided to reach to Dahn for advice on daily charging to optimize the battery pack longevity. The researcher responded: “I would recommend charging to 70% normally. When you need a long trip, charge to 100%.”

so will 70-80% over a 90% daily really help degradation?

 

[TexasEV]

so will 70-80% over a 90% daily really help degradation?

Statistically significant but not clinically meaningful.
In other words, if a couple of miles of range loss over many years makes a difference in your life, then perhaps you've bought the wrong car.

 

[Kenz]

Interesting videos on this topic. Short answer is 70% daily and more if needed for trips.
Fast Five: How To Keep Your Electric Car Battery Healthy - YouTube

IDEAL Tesla Battery Daily Charge Limit for your day-to-day driving as per Mr. Jeff Dahn - YouTube

 

[Cheesy23]

I go by what Jeff Dahn said who is working closely with Tesla on battery technology.

I quote him
"- Discharging to 5% state of charge (95% discharge) doesn't harm the battery either. Discharging all the way, which could be damaging, is actually prevented by the Tesla pack control electronics."

Here is the source:
Charging for optimum battery life | Tesla

So yes, it is perfectly fine to discharge your car to near zero in terms of battery health. I would highly recommend not aiming for lower than 10% for many reasons. But when it comes strictly to battery health and longevity, it is perfectly fine to go low.

So are you saying that it's better for the battery to go low (under 10%), rather than high (over 90%)?

 

[arnis]

So are you saying that it's better for the battery to go low (under 10%), rather than high (over 90%)?

Pretty much. %%% is not something battery cares. Battery cares about voltage between anode and cathode.
For Li-ion, going above 3.7V will start to accelerate degradation, very slowly.
Up to 4.0V. Then faster and faster as voltage raises. 4.5V is death sentence.
Normal operation range for most cells is 2.5V-4.2V.
At 10%, voltage is around 3.2V
And there are no known "accelerated degradation processes" happening at the low end of normal operation range.
There is degradation below 2.5V. Below 1V is death sentence
30% is actually near perfect storage state. It's far from low voltage end and far from 3.7V.
90% on the other hand is above 4V.

I've discharged my EV below 3.0V (0-5%) like 80-100 times and it has excellent capacity compared to fleet average. I've also charged above 4V (80%) like 100-150 times (therefore rarely).

 

[Viking1]

And there are no known "accelerated degradation processes" happening at the low end of normal operation range.

How about losing 1 RM / week? Does that qualify? Because it is certainly known to me. For a couple of months I let the charge drop to < 10% then SC to 90%. During this time I lost 1 RM/week.

If it hurts, stop it, so I did. Now I keep the charge at > 30%. Since that time (3 months ago) I have lost ZERO RMs.

Now it is possible that the reason for the rapid degradation was heat generated in the battery by SC from 10-90%. Whatever the case, I'm certainly not going back there.

 

[whttiger25]

How about losing 1 RM / week? Does that qualify? Because it is certainly know to me. For a couple of months I let the charge drop to < 10% then SC to 90%. During this time I lost 1 RM/week.

If it hurts, stop it, so I did. Now I keep the charge at > 30%. Since that time (3 months ago) I have lost ZERO RMs.

Now it is possible that the reason for the rapid degradation was heat generated in the battery by SC from 10-90%. Whatever the case, I'm certainly not going back there.

it's tough to judge what this means because "per week" is not a helpful part of the equation. What more important is how many miles you drove, or how many cycles you went through, to result in each loss of a RM.

So since you said a couple months, I assume you lost 8 RMs?

In addition I see you have a relatively new vehicle. The car tends to lose the most RMs in that 5000 - 15000 mile area, then slow down. So your loss in RMs could be more correlated to this expected degradation as opposed to your charging habits.

 

[arnis]

How about losing 1 RM / week? Does that qualify? Because it is certainly known to me. For a couple of months I let the charge drop to < 10% then SC to 90%. During this time I lost 1 RM/week.

Well you did charge to 90% at SC each and every time you discharged to 10%. So no, that doesn't qualify.
I'm pretty sure that charging itself for so long (therefore hot) and so high voltage (4.2V in case of Tesla) did that mostly.
Also @whttiger25 is right. Degradation is extremely fast for few dozens of cycles of battery lifetime.
Also RM is imaginary number. Has little to do with how much capacity there actually is.
If you store your vehicle for a year and then start driving, it will lose those RM's during few charging cycles.
Actually, capacity was lost during a year, not during few days.

 

[Viking1]

it's tough to judge what this means because "per week" is not a helpful part of the equation. What more important is how many miles you drove, or how many cycles you went through, to result in each loss of a RM.

Around 200-250/week. I was only charging that the SC, once every week.

So since you said a couple months, I assume you lost 8 RMs?

Yes, about that.

In addition I see you have a relatively new vehicle. The car tends to lose the most RMs in that 5000 - 15000 mile area, then slow down. So your loss in RMs could be more correlated to this expected degradation as opposed to your charging habits.

OK, but is was dramatic. I started this around 6K and ended it around 8K. From 1 RM/week to 0 since that time. It is like someone flipped a switch. Could also have something to do with my 90 battery. I've not read this issue for 85 batteries. Anyway, as I said, I don't care to try to repeat that experiment.