Some data on capacity loss.

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sdobbie

Member
Joined
May 31, 2015
Messages
22
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
 
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.
 
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.
 
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-i3-long-term-battery-capacity-report-better-expected/

Also this so called expert, has just made himself look , like a 'complete fool'
https://de.slideshare.net/DavidQuarles/bmw-i3-vs-tesla-battery
His inference and the facts are just 100% the opposite
 
EVMan said:
Also this so called expert, has just made himself look , like a 'complete fool'
https://de.slideshare.net/DavidQuarles/bmw-i3-vs-tesla-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:
 
Oleksiy said:
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 said:
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".
 
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 said:
EVMan said:
Also this so called expert, has just made himself look , like a 'complete fool'
https://de.slideshare.net/DavidQuarles/bmw-i3-vs-tesla-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:
 
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 said:
Oleksiy said:
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 said:
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".
 
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.
 
Lhs165 said:
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.
3.7 V might be the cell's voltage at 50% charge level. Another way of looking at 3.7 V is that it is the average voltage over the cell's full 0% - 100% charge level range.

Lhs165 said:
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.
If a manufacturer uses a cell's maximum voltage to calculate the cell's and thus the battery pack's capacity, that would be dishonest because a cell's voltage drops as its charge level drops.

Lhs165 said:
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.
I don't think one can use a voltage ratio to calculate a usable capacity. Although 3.7 V is the nominal voltage, it is not the maximum voltage that the battery management system (BMS) considers to be "full". Electric Vehicles and the i3 (60Ah and 94Ah) lists the allowed battery cell voltage range to be from ~3.4 V to ~4.0 V at 72º F.

Lhs165 said:
Short answer is we do not charge to “100%” ever.
True. The BMS doesn't allow the actual charge level to drop below ~10% (an indicated 0%) or to rise above ~95% (an indicated 100%).
 
Just purchased a used i3 BEV 60Ah 2014.
Electric Vehicles and the i3 (60Ah and 94Ah) lists that taking Kapa. Max. (maximum battery capacity) readings can differ depending on weather conditions.
My data in Latvia
03/09/2018 40100 16,5 kWh
10/09/2018 40300 16,7 кWh
 
Batt.Kapa may depend on the ambient and/or battery temperature, but I'm still to see any influence of these factors in my case. The data I've logged yet doesn't show any correlation, maybe I need to see more significant swings in temperature. See my report on this in this thread http://www.mybmwi3.com/forum/viewtopic.php?f=3&t=5392.
 
Oleksiy said:
Batt.Kapa may depend on the ambient and/or battery temperature, but I'm still to see any influence of these factors in my case. The data I've logged yet doesn't show any correlation, maybe I need to see more significant swings in temperature.
According to Electric Vehicles and the i3 (60Ah and 94Ah) the i3 LMo-NMC battery cells operates at a cell voltage range of 2,7V-4,125V (nominal cell voltage of 3,7V), but below 10% absolute battery SOC the sell voltage falls off very rapidly and battery manufactures reserve this capacity to avoid damaging battery cell. Cell voltage for battery pack at the 10% absolute is 3,45-3,5V. The battery capacity was between the lower 10% absolute SOC and a maximum value of between 89,9 and 92.3% (4,05 - 4,1V) depending upon temperature (-17 to 37 degC): the difference amounting to some 2,2kWh (18,834-16,626 kWh) between very cold and very hot. Between the bottom and top end margin is the nominal usable battery capacity and this one that car displays. In actual battery capacity isn't unchangeable value but depends upon ambient temperature and upon driving style and speed (how the battery was discharged in past). To sum up battery usable capacity (Kapa. Max.) varies with cell temperature and discharge rate (C-rate)
 
Thanks, this is very helpful. It means my battery will go down to mid-16 kWh in the frosty winter days, and then may recover in spring and summer to some 17+ values (average of 18 kWh observed during this summer minus some expected degradation). I'll report once I have supporting stats.
 
A fully charged lithium ion battery will always ready 4.0v in a idle state and 3.4-3.7v under load, normally 3.6v. Its how Dewalt scams people that their tools are 20v when really they are 18v (5 cells x 3.6v), they are 20v in an idle fully charged state but can not be more than 18v under load.
 
After doing a 'Departure Time' charge , my Batt.Kapa.Max now indicates 18.4 . That's the highest I've seen for awhile . It's clear that the battery is brought up to optimum temperature during the 'Departure Time' charging process . Is this a good way to get the best Batt.Kapa.Max reading possible ? Would the 'Departure Time' charge process cool the Battery to bring it below 40C in cases where it is above that ? My 2016 has about 32k Km or 20k miles and has been on the road just over 2 years .
 
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