How much will my battery degrade after two years of charging to 100% almost every night?

[BoltEV]

Background: I reviewed this Forum and others to determine how best to charge my Chevy BoltEV after I acquired it two years ago.

Many posters to this forum warned to not charge it everyday and to use Hilltop Reserve to keep from charging to 100%.

Some would link to a dated technical discussion of how Lithium Ion batteries will degrade in performance if charging were done to 100% consistently.

I noted that none of these “experts” drove a GM product; most of them drove the Nissan Leaf, or a Mercedes compliance car, etc.

Rather than not utilize the full capabilities that I purchased and having the confidence in GM after their experience with the Spark and the Volt 1.0, I chose to charge my BoltEV to 100% virtually every night.

It is now the 2 year anniversary of my acquisition and I wanted to determine its performance and the effect of battery degradation, after driving an average of 1,000 miles per month.

So, I drove yesterday with the following performance options:

With temperatures ranging from 68-74 on the outgoing drive, I kept the fan on, but turned off the heating/cooling. In the evening drive to return, the temperatures ranged from 48-54 and again I kept the heating/cooling off, but for the last hour of the drive used the seat and steering wheel warmers.

I drove in “L” and used cruise control when safe and feasible between 55-65 outgoing and 50-65 in the evening drive on my return. There were times I of course drove above 70, but I tried to keep this to a minimum.

The lights were automatically turned off on the drive out but automatically were on on the evening drive home.

I of course listened to the radio. I did not use the Low Power option when it was offered to me but the car did go into low propulsion mode on the final leg of the trip. I then turned off the seat and steering wheel warmers.

The results:

Miles driven: 264.1

Energy Used: 55.5 KWh

NOTE: I have attempted to attach photos of the relevant start/stop screens (jpegs from 73 to 228 KB), but I cannot seem to get them to view.

 

[GetOffYourGas]

Does this imply that you lost a few kWh of capacity? Looks like 10-12% loss. You probably didn’t do this test run when the car was new so we don’t have a baseline to compare to.

 

[BoltEV]

I read this as no loss at all!

The only comparison that is relevant is a car rated at 230 miles per charge when new, easily exceeds that 2 years later.

I drove 264 miles!

10-12% loss means I would have run out at 53.8-54 HWh. I was going strong at 55.5!

Mathematically I had 20 more miles to go before the battery was empty.

I was not in the mood and too tired to drive it to zero.

 

[SeanNelson]

The results:

Miles driven: 264.1

Energy Used: 55.5 KWh

I don't see how this says anything about capacity loss - all it tells us is (a) how efficiently your drove, and (b) your battery holds at least 55.5kWh. To get an idea of capacity loss, you'd have to look at the state of charge of the battery at the end of the drive, use the kWh to extrapolate the total battery capacity, and then compare that to the same metric from when the car was new.

For example, if you had a 5% charge left at the end of that trip, and assuming that you started with 100% charge, that means that the 55.5kWh you used for the trip represents about 95% of your battery (100% - 5%). That, in turn, would tell you that the battery has a capacity of approximately 58.4kWh (55.5 / 0.95). If you could compare THAT number to a similar measurement taken when the car was new THEN you'd have some indication of capacity loss.

In practice, the capacity figure you get by doing this bounces around somewhat, so you'd have to take the average of several readings to get a sense of what's happening with the battery.

 

[BoltEV]

This proves that my decision to charge to 100% most every night has been vindicated.

 

[BarfOMatic]

This proves that my decision to charge to 100% most every night has been vindicated.

No, it means you managed to drive 264.1 miles one day. Nothing more, nothing less. Maybe the exact same drive on a similar day (same route, temp, rain/cler, humidity, wind speed and direction, etc.) when the car was new would have left you with 25% battery remaining at the end of the drive, instead of it being almost empty.

N.E.D. : Not Enough Data.

 

[BoltEV]

Of all the 264 mile trips I have taken over the last two years, I never had 25% of the battery capacity remaining. Thank you.

 

[BoltEV]

Next time I will settle the debate by using the My Chevrolet app at the end of the drive to tell me the remaining capacity.

 

[GetOffYourGas]

You are attempting to "prove" something with a single data point. A somewhat poor one, at that.

Now if the car's performance and range continues to meet your needs, then the condition of the battery is good enough. If that's what you've proven, then that's fine.

After driving a Leaf for 5.5 years, I was down to ~80% capacity, but I still could get far enough for my needs. Does that mean that my charging habits were "vindicated"?

 

[BoltEV]

After driving a Leaf for 5.5 years, I was down to ~80% capacity, but I still could get far enough for my needs. Does that mean that my charging habits were "vindicated"?

My understanding from anecdotal evidence supplied by Leaf 1.0 owners on this forum, is that more cautious charging habits would have lessened your 20% degradation of your battery capacity after 5.5 years. Whether that is true or false and whether you were willing to go to that extra effort is only for you to decide.

I don't have a Leaf 1.0; I have a GM Chevy Bolt EV.

I preferred to not believe the "shy is falling" arguments given anecdotally by other car owners on this forum (and other forums) and chose instead to believe research that I separately did.

This research lead me to believe that GM incorporated its experiences from the Spark and Volt and built a battery system that, among other features, put a headroom of X percent and a floor of Y percent into the Bolt battery to then give the user a 60KWh usable capacity.

Consequently, the degradation of lithium ion would most likely occur, at least initially, within these protected areas, and hence I should not see any degradation for many years.

It is my belief that this has borne true for my first two years of driving with "aggressive" charging habits.

Other than the stated capacity of 60 KWh when the car was delivered new, I cannot go back in time and give any other data point for you to measure against.

I am, willing to consider more testing of my vehicle, under more specified conditions of others "in the know" so that I can get a clearer picture of the current capacity of my battery.

As I mentioned earlier, I should have looked to the My Chevrolet app for the percentage charge remaining.

Had I not been tired in the late evening after driving 264 miles, I would have considered doing what I did when my Chevy Volt 1.0 lease was about to end: drive it until the battery is completely empty, so that we would know the full capacity based upon the Energy Used meter.

If you have some of those specified conditions for me to consider on another test: fire away!

I will say that, somewhat analogous to your stated question, that if my Bolt EV was able to deliver 60KWh and mileage of 230 miles on an "average" drive when new on delivery, that, yes: if I can now get at least 55.5 KWh and 264 miles while doing an acceptable "regular" drive; I am happy with my "charging habits!"

For those interested and who know Southern California, the drive was:

Outgoing: the 170 south to the 134 east to I-210 east to I-10 east, when in Yucaipa I noted that there was a beginning of elevation, so that I turned around back on the I-10 west and 210 west until I had completed 105 miles and stopped for dinner and some poker.

The Return: 210 west to 134 west to I-5 north to 118 west to 23 south to 101 South to 134 east; turning around just after Glendale to 134 west to 170 north and off to home for the remaining 159 miles.

 

[SeanNelson]

Next time I will settle the debate by using the My Chevrolet app at the end of the drive to tell me the remaining capacity.

Yes, the remaining capacity and the kWh used (along with the starting capacity, which I assume was 100%) will give you much better information on what the actual capacity of the battery is. But without similar numbers from when the car is new it won't tell us anything about whether the battery has degraded or not.

I'm not trying to argue that the battery hasn't held up well in the face of 100% charging. And I have no doubt that you're pleased with the range you're getting. But with the information you gave us I think you'll find it hard to convince most folks anything about battery degradation without more concrete data.

 

[BoltEV]

Thank you Sean.

So you are not convinced that we all have the same 60KWh capacity when new?

 

[SparkE]

Thank you Sean.

So you are not convinced that we all have the same 60KWh capacity when new?

I have seen posted Torque Pro logs from other people, that they had taken when the Bolt was brand new, and a few were over 60 kWh, most were in the 57-59.x kWh range. It apparently does vary, by up to several percentage points.

 

[BoltEV]

If after two years my capacity > than 60 KWh, then I am all smiles in spite of how much greater it was when new!

So I see no point in driving it until exhausted, because there will always be someone here with a contrarian view point, since there is no way to know hiw many KWh’s it had at new.

I will say this: in the used marketplace, the exact amount of battery capacity will be important irrespective of how much its capacity was at new.

So I take the same viewpoint: how much capacity I have now is the critical factor. Not how much I may have had when new.

 

[SeanNelson]

So I see no point in driving it until exhausted, because there will always be someone here with a contrarian view point, since there is no way to know hiw many KWh’s it had at new.

If you're a buy-and-hold person like I am and intend to keep your Bolt for a while, you might want to get a good idea of your current capacity now so that in the future you'll have some idea of how your battery is degrading from this point forward. It's not something that I personally am terribly concerned about, but to each his own.

 

[BoltEV]

Like you, I tend to hold a car for 12 years.

However I look at an electric car as “technology” and this is my second three-year lease, after my Chevy Volt.

I have to make a decision in one year, and the hope for $35,000 model 3 appears to be vaporware! Haha

My residual is $25,000: so I’m not too optimistic on that front either.

I’ll just have to see what’s available in 12 months.

In any event, how do you suggest I take that measurement now?

 

[theothertom]

However I look at an electric car as “technology” and this is my second three-year lease, after my Chevy Volt.
I have to make a decision in one year, and the hope for $35,000 model 3 appears to be vaporware! Haha

I've owned cars for 50 years and never leased one, until now. Technology is changing so quickly and I don't want to be "stuck" with very outdated technology.
The $35K Model 3 is projected to have a 50KW battery, so the Bolt is better in that regard. VW, BMW and Mercedes have aggressive plans to introduce models with ~400 mile range next year, but I would probably wait until 2021 for them to work the bugs out.

 

[SeanNelson]

...how do you suggest I take that measurement now?

I described the method in my first post in this thread.

 

[BoltEV]

The $35K Model 3 is projected to have a 50KW battery, so the Bolt is better in that regard. VW, BMW and Mercedes have aggressive plans to introduce models with ~400 mile range next year, but I would probably wait until 2021 for them to work the bugs out.

I predict that Tesla will never release a $35,000 Model 3.

Their financial problems dictate that they must continue to sell the more expensive models with the greater profit margin into the foreseeable future.

 

[BoltEV]

...how do you suggest I take that measurement now?

I described the method in my first post in this thread.

Yes, I recall, but your method requires that I have a comparison measurement to when my car was new, which I never took.