keep car charging to 90% or 50% at home ? for driving every day

[Tam]

...The reduction, limiting and backtracking Tesla has done recently particularly to older batteries shows that they are seeing the degradation and feel it's necessary to limit down those old batteries to prevent them from suddenly fail...

The batterygate lawsuit is not about degradation but it claims Tesla wants to reduce the risk of spontaneous battery fire by making the battery less powerful (thus, reducing the range) by preventing owners from being able to charge to its fullest:

"The lawsuit points to a recent spate of Tesla battery fires, and claims that instead of informing its customers about a potential fire risk, the company "chose to go behind the backs of its customers and use software updates and throttling of the battery to avoid liability."

...But after owning my Model S for 6 years and putting 260k miles on it I have seen the effects first hand. I'm not fear mongering...

260,000 miles? The warranty counts on 12,500 miles per year but you are driving more than 40,000 miles a year!

You are scaring all those in the infinity mile battery warranty department!

 

[David99]

The batterygate lawsuit is not about degradation

Yes the reduction in range is artificial, thus not degradation. But it is a condition the battery has developed over time and use and has prompted Tesla to act on it with some pretty drastic limitations to the car. We don't know what exactly Tesla has found. I think it would be in every owner's interest to avoid getting their battery in the same state. I can tell from experience this is pretty severe.

260,000 miles? The warranty counts on 12,500 miles per year but you are driving more than 40,000 miles a year!
You are scaring all those in the infinity mile battery warranty department!

The warranty for the 85 battery was always unlimited miles. It never counted on any specific number of miles driven per year. But either way, there are affected cars that have far less miles and use. I believe the reason I was able to go unaffected for 240k miles (that's when I got hit even thought I had the software installed for months before) is because I was following the recommendations I wrote about above. I'm not trying to scare anyone. I'm pointing out there is something starting to appear that every other comment here just ignores.

 

[DoctorVenkman]

The battery chart is not for an EV, it is for Li-ion battery in general and is probably made by someone with en engineering degree, or at least someone in the rechargeabe battery business. It looks correct as is.

I don't doubt the validity of the research done, what I am saying is that that graph is incredibly misleading if you are trying to draw conclusions vis-a-vis EV battery degradation. Let's take a look at the bottom (black) and top (orange) data series for example.

If we're assuming a Model X 100D, at 1000 cycles the orange line represents driving about 30,000 miles ( = 300 mile range * 10% usage * 1000 cycles) while the black line represents driving 225,000 miles (= 300 mile range * 75% usage * 1000 cycles). However, the equivalent point in the x-axis on the orange line for miles driven would be 7,500 cycles, since that is also equivalent to driving 225,000 miles.

So for an apples-to-apples comparison, you'd have to look at the black line at 1000 cycles and the orange line at 7500 cycles. From there you would see... a whopping 2% difference. So for all the pain and effort of keeping your car in the optimal 65% to 75% range, you gain 2% battery capacity after 225,000 miles driven compared to charging to 100% every day.

That chart actually PROVES that there is almost no difference between charging to 100% and keeping your battery in the optimal range. If you're the type that cares about 2% additional degradation over 225,000 miles then go ahead and keep your battery in the optimal range, otherwise don't worry about it. It has almost zero impact.

 

[Kenz]

Keep the battery between 20 - 80% most of the time. 70% may be a little better.
Other than that just drive it and enjoy. On long trips it is OK to go above or below your daily range if needed.
Don't charge to 100% and let the battery sit full for hours or days. Level 2 charging is easier on the battery than SuperCharging so most, the majority, of your charging should be at home or work on level 1 or level 2 chargers.

 

[David99]

If we're assuming a Model X 100D, at 1000 cycles the orange line represents driving about 30,000 miles ( = 300 mile range * 10% usage * 1000 cycles) while the black line represents driving 225,000 miles (= 300 mile range * 75% usage * 1000 cycles). However, the equivalent point in the x-axis on the orange line for miles driven would be 7,500 cycles, since that is also equivalent to driving 225,000 miles.

Your numbers are a little off here. I have driven 265k miles and aprox 1900 cycles (according to CAN bus). How on earth is 225 k miles 7500 cycles?

 

[DoctorVenkman]

Your numbers are a little off here. I have driven 265k miles and aprox 1900 cycles (according to CAN bus). How on earth is 225 k miles 7500 cycles?

I'm referring to this graph that was posted on the first page:

It's from a scientific test done to measure the effect of SoC on battery degredation. They tested how various SoC discharge cycles impact battery capacity. See how the orange line is testing only 10% discharge on each cycle? It's not meant to reflect real-life usage. The more "real life" lines are the green, light blue, and black ones, since they involve more discharging.

My point is that to make any accurate assessment of EV charging habits, one must convert the x-axis to miles driven rather than charge cycles. Each line represents a different amount of miles driven. Even the "optimal" orange line is only 2% better than the "worst" black line, when compared on a miles-driven basis.

The main difference in battery capacity really comes in the 3000+ cycle range, which is far beyond most people will ever drive their car. It's pointless to fret over what level you charge your car unless you plan on keeping it for 500k+ miles and care about ~5% range difference.

 

[eevee-fan]

I'm referring to this graph that was posted on the first page:

It's from a scientific test done to measure the effect of SoC on battery degredation. They tested how various SoC discharge cycles impact battery capacity. See how the orange line is testing only 10% discharge on each cycle? It's not meant to reflect real-life usage. The more "real life" lines are the green, light blue, and black ones, since they involve more discharging.

My point is that to make any accurate assessment of EV charging habits, one must convert the x-axis to miles driven rather than charge cycles. Each line represents a different amount of miles driven. Even the "optimal" orange line is only 2% better than the "worst" black line, when compared on a miles-driven basis.

The main difference in battery capacity really comes in the 3000+ cycle range, which is far beyond most people will ever drive their car. It's pointless to fret over what level you charge your car unless you plan on keeping it for 500k+ miles and care about ~5% range difference.

I made the same mistake as you did in assuming one 20% discharge as one cycle. If you use only 20%, it takes 5 partial cycles to equal one cycle. So... the chart is correct as is... see link blow on measuring battery test cycles of Apple laptops.

Determine battery cycle count for Mac notebooks



BTW...

 

[DoctorVenkman]

I made the same mistake as you did in assuming one 20% discharge as one cycle. If you use only 20%, it takes 5 partial cycles to equal one cycle. So... the chart is correct as is... see link blow on measuring battery test cycles of Apple laptops.

Determine battery cycle count for Mac notebooks

Nope. Apple's cycle counting methodology isn't really relevant to the research paper quoted.

If you look at the actual research paper (linked here) it's pretty clear that each DST cycle on the graph only represents the SoC discharge range, not a full discharge:

"For each test, the cell first starts at a set SoC level and the DST profile is applied repetitively until the set stop level is reached. The cell is then recharged back to the starting level at a 1 C-rate to finish one test cycle"

Again, there is minimal impact (<5%) from SoC on battery capacity until you get into 500k+ mile territory. It's really not worth worrying about unless a ~15 mile range reduction after 500k miles driven bothers you.

 

[eevee-fan]

Nope. Apple's cycle counting methodology isn't really relevant to the research paper quoted.

If you look at the actual research paper (linked here) it's pretty clear that each DST cycle on the graph only represents the SoC discharge range, not a full discharge:

"For each test, the cell first starts at a set SoC level and the DST profile is applied repetitively until the set stop level is reached. The cell is then recharged back to the starting level at a 1 C-rate to finish one test cycle"

Again, there is minimal impact (<5%) from SoC on battery capacity until you get into 500k+ mile territory. It's really not worth worrying about unless a ~15 mile range reduction after 500k miles driven bothers you.

15 miles is not just 15 miles. It's 15 miles vs the other degraded mile.

OK, let's go with that, looking at the:
orange line 100% to 40% (60% DOD) with 1250 cycles to 90% capacity.
blue line 75% to 25% (50% DOD) with 3000 cycles to 90% capacity
purple line 75% to 45% (30% DOD) with 5000 cycles to 90% capacity.

Orange vs Blue vs Purple
1250 vs 3000 * 50/60 vs 5000 * 30/60 = 1250 vs 2500 vs 2500.

It is significant, but the truth is that most will be trading the car in before hitting that point. 1250 full cycles (15K annual miles / 250 miles per cycle = 60 cycles a year). With full DOD range of 250 miles, it would take 21 years (315K miles) for Orange and 42 years (630k miles) for Blue/Purple to degrade to 90%.

Key is not to charge to somewhere between 50-75% actual SOC whatever that equals to on the user interface, for the longest life possible.

Also note that the chart indicates increasing life another 44-130% when charging only up to 50%. So that'd be 60-100 years. :0

 

[Evstrat]

Like everyone is stating, you charge based on your driving situation. I have a daily 90kms round trip to work everyday, because I live in a climate, I personally charge to 90% during the winter months, and 80% during the summer. Has worked fine for me.

I personally wouldn't change to 50% for the fact that if you have a unplanned drive to do, you don't want to risk scrambling for charging.

And Faster charging is ideal...no need to slow it down unless you have no other choice.

The slower you charge the Battery the Better, of course, if needed charge as quickly as possible, but if you have the time for use 110 V and slow charge, I was told this by a Tesla engineer and causes less battery degradation, faster charging causes heat and thus increased degradation.