sdobbie
Posts: 15
Joined: Sun May 31, 2015 4:09 am

Some data on capacity loss.

Wed Sep 12, 2018 1:22 pm

Hello all,

I have a 2013 I3 with range extender and when I got it in 2015, it had 18.2 kwh available when I checked in the service menu. As time goes on this value varies quite a bit but always follows a downwards trend. When it reached around 16kwh one year, I reported it to BMW and after they sorted it, it went up to over 19. Again this followed a steady downwards trend and now I am at 16.2kwh. That is a 2.69 percent loss per year. Range has also decreased accordingly.

What I suspect is happening here is the capacity is being limited gradually by software so that BMW never have to replace the battery within the warranty period. Here is the data I have been recording. I haven't been recording it over the past two years, just observing.


18/10/15 19.4
21/10/15 19.5
31/10/15 19.4
09/11/15 19.3
20/11/15 19.2
29/11/15 18.9
30/11/15 19.2
01/01/16 18.5
13/03/16 18.6
15/04/16 18.5
09/05/16 18.6
17/05/16 18.6
09/06/16 18.6
14/08/16 18.6
25/08/16 18.1
12/09/18 16.2
Electric for ever more.

Elkjaer
Posts: 11
Joined: Fri Jan 08, 2016 12:25 pm

Re: Some data on capacity loss.

Wed Sep 12, 2018 1:37 pm

I see the same trend, though I noticed that estimated remaining kWh was reset at software upgrades performed by BMW.

Date Mileage (km) (kWh)
26 Oct 2016 19487 18,7
27 Oct 2016 19502 18,6
27 Oct 2016 19516 18,7
28 Oct 2016 19516 18,8
28 Oct 2016 19544 19,6
6 Nov 2016 19765 19,5
7 Nov 2016 19800 19,6
8 Nov 2016 19859 19,3
23 Nov 2016 20197 19,4
2 Dec 2016 20595 17,8
19 Dec 2016 21249 18,9
Apr 6, 2017 24936 17,6
22 Aug 2017 30547 17,3
30 Aug 2017 30836 17,1
24 Oct 2017 32893 17,0
9 Nov 2017 33495 16,5
15 Nov 2017 33678 17,0
11 Jan 2018 35574 16,9
22 Feb 2018 36590 16,6
4 Apr 2018 37231 16,6
6 Jun 2018 38758 16,7
25 Jul 2018 39466 16,4

Based on the trend in my own data I have forecast (assuming linear degradation- which is not the correct assumption) the remaining kWh to reach the warranty level (13,16 = 70% of 18.8 kWh) at 86000 km in around 4 years from now.

EVMan
Posts: 207
Joined: Sat Feb 25, 2017 4:31 pm
Location: USA, CA

Re: Some data on capacity loss.

Wed Sep 12, 2018 9:47 pm

When mine was new, it was at 19.7 for quite some time.
So while 18.8 kWh may be advertised, the software displayed 19.7 kWh as usable

My 2017 started with 29.8 KWH ,or as you can just say 30.
What data will BMW use to calculate max capacity ?

Weather and temperature , have a big effect , with capacity reduced with temperature, temporarily.

Re-setting the BMS , should not help, as it will eventually catch up with the true state of the battery.
Some used leafs were sold, with this bad act, and the cars quickly lost bars again

Re-setting will only help , if the BMS is not calibrated, and cannot decide the true state of battery.
e.g in Leaf 30KWH , they had a bug, and the BMS under reported the battery capacity.
Shame on Nissan, that people found about this first, and they had to react.

If resetting increases the capacity again , after 50 discharge cycles, i would think the BMS is not calibrated in i3 too.
Last edited by EVMan on Thu Sep 13, 2018 8:52 pm, edited 1 time in total.
2016 22KWH Rex ( Lease to Return ) ~ Model 3 Dual Motor, Long Range ( Wait-listed )
2017 33KWH Rex
Solar ToU Plan

EVMan
Posts: 207
Joined: Sat Feb 25, 2017 4:31 pm
Location: USA, CA

Re: Some data on capacity loss.

Thu Sep 13, 2018 8:52 pm

Actually if you think about this, any manufacturer , which buys battery and BMS from different vendors, will likely run into calibration issues. Lot of filed test will be needed for calibration.

While we see this significant detonator, this fan boy gets very different results, even after 70K miles ( 18.4) from us
https://www.bmwblog.com/2017/04/24/bmw- ... -expected/

Also this so called expert, has just made himself look , like a 'complete fool'
https://de.slideshare.net/DavidQuarles/ ... la-battery
His inference and the facts are just 100% the opposite
2016 22KWH Rex ( Lease to Return ) ~ Model 3 Dual Motor, Long Range ( Wait-listed )
2017 33KWH Rex
Solar ToU Plan

EVMan
Posts: 207
Joined: Sat Feb 25, 2017 4:31 pm
Location: USA, CA

Re: Some data on capacity loss.

Thu Sep 13, 2018 8:54 pm

My Data in California Weather
New 19.7 KWH
2 years/21K miles : 17.8- 18KWH
2016 22KWH Rex ( Lease to Return ) ~ Model 3 Dual Motor, Long Range ( Wait-listed )
2017 33KWH Rex
Solar ToU Plan

Oleksiy
Posts: 30
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: Some data on capacity loss.

Thu Sep 13, 2018 11:58 pm

EVMan wrote:Also this so called expert, has just made himself look , like a 'complete fool'
https://de.slideshare.net/DavidQuarles/ ... la-battery
His inference and the facts are just 100% the opposite

This guy may very well be right about the quality of the battery itself. In the real world though, BMW i3 and Tesla batteries are separated by completely different usage patterns. Tesla's packs enjoy moderate charging up to 80% and limited DOD (depth of discharge) on everyday basis due to the sheer size of the pack and presence of flexible charging settings in the system. And in our case people are constantly abusing their batteries by charging them up to 100% and discharging quite deeply, the range of the total pack being quite limited.

Also, even if we had the ability to limit the charging to lower than 100% due to our commuting needs, our car actively precludes us from doing so constantly striving to get to full charge by ignoring the off-peak time settings (my own experience).

And the notorious ABC strategy is adhered to by BMW i3 owners with religious obstinance, according to multiple answers in the FB group to any question on the best practices in charging. I understand this "always be charging" nonsense was introduced both by BMW in their manual, and by some book author - people keep quoting him as a founding father :roll:

alohart
Posts: 1350
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Some data on capacity loss.

Fri Sep 14, 2018 1:45 pm

Oleksiy wrote:And in our case people are constantly abusing their batteries by charging them up to 100% and discharging quite deeply, the range of the total pack being quite limited.

I'll preempt the replies that will state that an indicated 100% isn't the actual 100% charge due to an i3's BMS preventing charging to an actual 100%. What most i3 owners seem to believe is that the indicated full charge is quite a bit lower than it actually is. For the 60 Ah battery pack, only 18.8 kWh of 21.6 kWh is available, or ~87%. That means that the total unavailable charge level buffers total ~13% with ~10% reserved at the low charge level end (i.e., an indicated empty is actually ~10%). That suggests that an indicated full charge is approaching ~97% of an actual full charge. That's a very high charge level at which degradation occurs more rapidly than at lower charge levels.

Oleksiy wrote:And the notorious ABC strategy is adhered to by BMW i3 owners with religious obstinance, according to multiple answers in the FB group to any question on the best practices in charging. I understand this "always be charging" nonsense was introduced both by BMW in their manual, and by some book author - people keep quoting him as a founding father :roll:

BMW's calculation was likely that almost all of those who "always be charging" would not degrade their battery packs more than 30% before their battery pack warranty expires thus sparing BMW the significant expense of replacing battery pack modules under warranty. BMW also didn't want to limit the upper charge level limit too much because the already low rated range would be diminished. BMW certainly didn't want new EV drivers to be concerned about managing their battery pack charge levels, so "always be charging" is the most convenient advice. Unfortunately, this advice will almost certainly lead to faster loss of battery pack capacity than would occur if i3 drivers would make a minimal effort to charge to full only when full range is needed and to do so just before departing. We're already starting to see concern with dropping Batt. Kapa. max values that could be exacerbated by "always be charging".
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

EVMan
Posts: 207
Joined: Sat Feb 25, 2017 4:31 pm
Location: USA, CA

Re: Some data on capacity loss.

Fri Sep 14, 2018 3:47 pm

I understand and agree with what you saying, but 'battery- in the car context' to me, will mean a the complete package ( battery, chemistry, design, BMS, rules etc ) and not just a a cell.
This will include the decision of large capacity car battery , with leads to less cycles and not charging to 100% routinely vs smaller more battery , which leads to more cycles , and mostly charging close to full.

Otherwise you cannot compare an expensive large 64ah battery cell, designed to be put in serial vs 1 small cheap cylindrical cell , which is designed to be put in parallel along with 72 or more cells and costs 1/100 too.

The comparison has to be of the end results of the full package , to make sense.





Oleksiy wrote:
EVMan wrote:Also this so called expert, has just made himself look , like a 'complete fool'
https://de.slideshare.net/DavidQuarles/ ... la-battery
His inference and the facts are just 100% the opposite

This guy may very well be right about the quality of the battery itself. In the real world though, BMW i3 and Tesla batteries are separated by completely different usage patterns. Tesla's packs enjoy moderate charging up to 80% and limited DOD (depth of discharge) on everyday basis due to the sheer size of the pack and presence of flexible charging settings in the system. And in our case people are constantly abusing their batteries by charging them up to 100% and discharging quite deeply, the range of the total pack being quite limited.

Also, even if we had the ability to limit the charging to lower than 100% due to our commuting needs, our car actively precludes us from doing so constantly striving to get to full charge by ignoring the off-peak time settings (my own experience).

And the notorious ABC strategy is adhered to by BMW i3 owners with religious obstinance, according to multiple answers in the FB group to any question on the best practices in charging. I understand this "always be charging" nonsense was introduced both by BMW in their manual, and by some book author - people keep quoting him as a founding father :roll:
2016 22KWH Rex ( Lease to Return ) ~ Model 3 Dual Motor, Long Range ( Wait-listed )
2017 33KWH Rex
Solar ToU Plan

EVMan
Posts: 207
Joined: Sat Feb 25, 2017 4:31 pm
Location: USA, CA

Re: Some data on capacity loss.

Fri Sep 14, 2018 3:51 pm

I agree with you - That's a very high charge level at which degradation occurs more rapidly than at lower charge levels.

In fact , initially for the first year, i rarely charged to full and did a lot of DC charging. I saw no deterioration then.
After that i stoped doing DC charging , charged at night to full ( low cost charging) .and started to see rapid deterioration



alohart wrote:
Oleksiy wrote:And in our case people are constantly abusing their batteries by charging them up to 100% and discharging quite deeply, the range of the total pack being quite limited.

I'll preempt the replies that will state that an indicated 100% isn't the actual 100% charge due to an i3's BMS preventing charging to an actual 100%. What most i3 owners seem to believe is that the indicated full charge is quite a bit lower than it actually is. For the 60 Ah battery pack, only 18.8 kWh of 21.6 kWh is available, or ~87%. That means that the total unavailable charge level buffers total ~13% with ~10% reserved at the low charge level end (i.e., an indicated empty is actually ~10%). That suggests that an indicated full charge is approaching ~97% of an actual full charge. That's a very high charge level at which degradation occurs more rapidly than at lower charge levels.

Oleksiy wrote:And the notorious ABC strategy is adhered to by BMW i3 owners with religious obstinance, according to multiple answers in the FB group to any question on the best practices in charging. I understand this "always be charging" nonsense was introduced both by BMW in their manual, and by some book author - people keep quoting him as a founding father :roll:

BMW's calculation was likely that almost all of those who "always be charging" would not degrade their battery packs more than 30% before their battery pack warranty expires thus sparing BMW the significant expense of replacing battery pack modules under warranty. BMW also didn't want to limit the upper charge level limit too much because the already low rated range would be diminished. BMW certainly didn't want new EV drivers to be concerned about managing their battery pack charge levels, so "always be charging" is the most convenient advice. Unfortunately, this advice will almost certainly lead to faster loss of battery pack capacity than would occur if i3 drivers would make a minimal effort to charge to full only when full range is needed and to do so just before departing. We're already starting to see concern with dropping Batt. Kapa. max values that could be exacerbated by "always be charging".
2016 22KWH Rex ( Lease to Return ) ~ Model 3 Dual Motor, Long Range ( Wait-listed )
2017 33KWH Rex
Solar ToU Plan

Lhs165
Posts: 2
Joined: Fri Mar 30, 2018 6:06 am

Re: Some data on capacity loss.

Mon Sep 17, 2018 1:27 pm

I maybe missing something. I found a picture of the 3.7 volt 94ah 350 wh battery cell that is in the 2017 33 kWh battery pack. On this picture it shows that the cell can go up to 4.15 volts. At 4.15 volts the cell would be charged to 100%. But the capacity rating of 33kWh is at 3.7 volt per cell. There are 96 of these in the pack. So 96 x 3.7 x 94 = 33,388.8. Number of cell times volt of cell times amp hour of cell. Or 33kWh. Or another way is 350 x 96= 33,600. Watt hour of cell times number of cells. Or 33kWh. It appears that BMW is figuring the capacity at 3.7 volt per cell and not 4.15 volt per cell like some other car manufactures. So if 4.15/100 and 3.7/x then when we charge to “100%” we are actually only at 89.15% and that is if they give of all of the 33kWh which they don’t. Short answer is we do not charge to “100%” ever.

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