Electric battery degradation

As I understand it, when not charging at all the cycles will be about 26%< >20% SOC unless you go a long decent stretch. So Jeff N statement is valid.

 

So you think that going from 20 to 26 % maybe 20 times in a day would create less "wear" than going from 80% to 20% maybe once or twice ?
I don't think that's a given either.

 

Yes.
Remember that when functioning like a regular Prius, the discharge rates are much much lower.

 

thanks jeff.

 

It's not a given, but it's likely. As a general rule, using a bigger chunk of the battery, higher average temperatures, and higher average SOCs will all result in a larger decline in capacity at some point in a battery's lifespan .

http://www.nrel.gov/docs/fy13osti/58550.pdf

http://www.nrel.gov/transportation/energystorage/pdfs/45048.pdf

 

Together with a Ph.D. student (focusing on smart energy management) I now plan to write an article about charging behaviour and battery degradation in real life situations, based on real life empirical data (see also what is sketched in the quote above). We will make the article available for everybody. The more empirical data we can use, the more solid this article will become.

So therefore a request to any of you. Could you send us data of your charging sessions over the years? It is important that for each charging session the amount of Wh input is given and kept separate from other charging sessions, so, for example, not adding different sessions on the same day. The data will be used in an anonymous manner, but a general acknowledgement will be included. Please send these data to [email protected].

 

Just completed charging form charge point, used 2.528 KWh to fully charge. Plugged in with .7 miles left, almost empty. Does anyone know if this is normal for a 2013 pip with 50 k miles on it? Just curious, thanks.

 

This not so easy to say. In the posts above, started with the post #38 of giora, and continued by me in post #42, we used situations in which the battery is as empty as possible. Do you also have charging data about such situations?

For the case you mention you first have to estimate how much available charge was still in the battery. What was your total EV range as indicated originally? Maybe it was 10 miles? Assuming that, you would still have 0.07 or 7% of available charge at the start of the charging session. Then you can divide the 2528 Wh by 0.93, which gives 2718 Wh. This number may seem a bit low. How many EV miles did you do in total of your 50k? And what was actually the total EV range as indicated after the previous charging session? Besides, the way in which the EV range estimation is determined by the car may also not be so linear as would be needed in these calculations.

You see, it is more complicated to do such calculations when still some charge was left. Maybe you can have data for cases with empty battery as well?

Jan

 

Jan,
Thanks for the reply. I have a different situation. I travel approximately 60 miles each way to work with a 5500' mountain in between at the 30 mile point of the trip. I regenerate for about 8 miles downhill. Due to this my daily estimated range on gauge is 24.8. This allows me to run in EV mode for the second half of the trip. (30-32 miles depending on traffic) I have about 14,300 EV miles of the 51,000 miles. Yesterday I used all the charge 0 miles of EV ( all bars on gauge were lit) after complete charge 2.58kw on charge point.

I am very happy with the results. Thanks to all for this forum. Great info and humor.

 

So, if I interpret your numbers well, the 0.7 miles left was from 24.8 initially, which is 0.028 or 2.8%. Then dividing 2528 would be by 0.972 (which is 1 - 0.028 ); this gives 2601 Wh as an estimation. This indeed is quite close to the observed 2580 Wh you mention today. These numbers are a bit lower than I see from other people. I cannot imagine that we have to blame your twice-a-day mountain for that?? Or is it due to degradation because of a larger number of EV miles you already made?

Do you remember these numbers when you just had the car?

 

Jan,
I can't recall for sure, however 2.74 keeps coming to mind after a complete charge.

This is my wife's pip.

I will check mine next time I drive it to Vegas and report back.

What are you seeing from others?

If it is degradation I am ok with it. Thanks again. I know I learn so much from everyone.

 

What I see from some others (including myself) is that initially the maximal charging sessions use just above 3000 Wh from the net and due to degradation this is estimated to decrease by about 1.5% to 2.5% per year (when per year between 2000 and 3000 EV miles are made). Below you see graphs of two different cases of which the first one is from myself.

If initially your wife's maximal charges took 2740 and now 2580, then this would be a degradation of about 6% up till now, which seems in line with the other estimates, as in your wife's case the number of EV miles per year and the number of charging sessions (including the mountain descent charging sessions twice a day) is higher. Also the outdoor temperatures will play a role. Probably later this summer still higher numbers will be reached, and using these numbers the estimated 6% can become a bit lower.

But I wonder why this initial number 2740 is 9% lower than the 3000 seen in other cases.

 

Jan,

I was thinking about disconnecting the 12v battery to reset the estimated EV miles and check the charge after a trip. Just a thought. Any ideas?

 

I think this will not affect the charge, only the prediction of the EV range that you will have. This prediction is usually based on your past driving behaviour, but after reset it is based on some rather arbitrary default value.

 

You are probably correct. I do recall that now that you mentioned it.

 

By the way, which month in 2013 did you start with this car? Then I can calculate more precisely the period between then and now.

 

October 2013.

 

i think i've lost about 10%, most of it the first year. mine is 3 years old, with 29,000 miles, 20,000 of which is ev.

 

Soon I will post an overview of estimations of the capacity loss percentage against the number of EV miles. I have 6 cases available now, but for one of them (from CharlesH) I do not yet have the EV miles. More cases for estimated loss percentage and EV miles over a given period are still welcome. What is posted I will include in the overview.

 

This post shows an overview of six cases for which a capacity loss percentage was estimated based on the maximal kWh input during charging sessions. These six cases are from bisco, CharlesH, giora, Potorap (wife's car), myself and from another person in the Netherlands. I have estimated the loss percentages on an annual basis.

The average of the six cases is 2.8%; the six numbers are 1.3%, 2.5%, 2.8%, 3.2%, 3.3%, 3.7%.

Probably two important factors affecting this percentage are the number of EV miles per year, and the climate. The number of EV miles directly relates to the number of charging sessions (including the downhill charging sessions), and it is generally assumed that this number has an effect. Therefore I also made a graph relating the above percentages to the annual numbers of EV miles; see below.

This graph (with red trend line) indeed suggests that for about 2000 EV miles per year the estimated annual percentage is around 2% to 2.5%, whereas for 6000 and more EV miles per year the estimated percentage is more around 3.5%. But the number of points is rather low, so too strong conclusions should not be drawn at this point. I still welcome data for more cases (maximal input Wh over the years or estimated loss percentage, and EV miles per year).

For the climate I did not make a similar graph, as it is not easy to represent climate in just one number. However, I think the effect of climate can be seen at least in my own case (the lowest percentage: 1.3% per year). I live in an area north of Amsterdam called North-Holland-North which is surrounded by sea (West, North and East: a peninsula) with a very mild sea climate, and the latitude is 15 degrees closer to the North pole than the locations of most others represented here.