Unclear Battery Report - What is the Capacity??

[gsutiger2]

PLEASE HELP!

2015 BMW I3
BEV
63,000 miles
My commute - 52 miles/83 KM per day mainly highway

I received the attached battery report today from BMW. Since the miles are pretty high, a detailed battery report was requested along with any battery warranty claims.

• Is this report actually providing the actual state of health?
  If yes, is it reading at 70% or 63%?
  Are these too low :? ?
  
  
  Link to Battery Report - https://ibb.co/SXJ11Br
  PDF of Battery Report - https://documentcloud.adobe.com/link/track?uri=urn:aaid:scds:US:75908ccf-d88d-4c7b-ba0b-e844433b47ff
  
  PLEASE HELP Many Thanks!

 

[eNate]

This is hard to read on my screen but it just looks like they're reporting the current state of charge, and what the state of charge was at different points over the last few days. I'm not seeing anything that looks like battery capacity.

 

[alohart]

UPDATE: My logic below is flawed. See this post for my correction. Thanks, 3pete, for pointing out my logical error!

My interpretation assuming a 60 Ah battery pack follows.

The full length of the linear bar chart on page 4 of the report shows the full 0% to 100% real charge level range of the battery pack which is greater than the charge level range displayed on the instrument panel due to low and high charge level unavailable capacity buffers. The battery management system (BMS) is limiting the usable charge level range from a minimum real charge level of 8% which is displayed as 0% to a maximum of 71.23% which is displayed as 100%. The top of the black portion of the charge shows the current 91.60% displayed charge level which is a 66.3% real charge level.

The note states that due to battery pack age, the maximum charge level isn't as high as it was when the battery pack was new which reduces the usable capacity. 18.8 kWh / 21.6 kWh = 87% of a new battery pack's capacity is usable with 13% being unavailable. This report indicates that 71.23% - 8% = 63% is currently usable, so 87% - 63% = 24% of the new usable capacity is no longer available. The usable capacity loss would need to exceed 30% to trigger a battery pack replacement under warranty.

It's unclear to me whether the reduced usable capacity is solely due to battery cell degradation or partially due to the BMS decreasing the usable capacity, possibly to decelerate the battery cell degradation rate in hopes of preventing a battery pack warranty claim. We know that the BMS can be reset using BMW's ISTA+ maintenance software. This frequently immediately increases the usable capacity, probably by decreasing the size of the high charge level unavailable capacity buffer that is controlled by the BMS. Indeed, many who have paid BMW dealers to measure the usable battery pack capacity have discovered that the usable capacity had increased to such an extent that a battery pack warranty claim was not warranted. This suggests that at least some of the usable capacity loss can be due to the BMS. The battery pack warranty guarantees that battery pack degradation doesn't exceed 30% which wouldn't include any buffer size changes made by the BMS.

I feel that BMW shouldn't be decreasing the usable capacity and thus our range just to reduce the number of battery pack warranty claims. Some Tesla car owners have sued Tesla for reducing their battery packs' usable capacity without their permission. We should be able to use all the range that our battery pack can provide while maintaining the same low and high charge level unavailable charge level buffer sizes as existed when our i3's were new. If this would lead to more battery pack warranty claims, so be it. We shouldn't have our range decreased to protect BMW from battery pack warranty claims.

If the usable capacity of our battery pack hasn't decreased by more than 30% by the time our battery pack warranty expires, I plan to reset the BMS using ISTA+ to try to increase the usable capacity a bit.

 

[gsutiger2]

Dear Aloha,
You are awesome! I agree, it is unclear. Having 24% of battery gone is not a good sign. Plus, at 63K miles, it will only get worse with my highway driving at 70+MPH.

I asked them to drain the battery and give me an actual percentage of the batteries SOH. IM finding the service technicians making up answers instead of elevating inquiries. Its as no one has seen an I3 in the BMW dealership or service area.

Thanks again!

 

[3pete]

Having 24% of battery gone is not a good sign.

Indeed that is not a good sign if it causes concern for your driving needs. I'm curious: have you done a batt. kapa max reading from the car's service menu? Or a SOH reading from an app like "electrified"? I'm estimating batt kapa max should be somewhere around 13.5kWh?

Also, what did the dealer do to get this report, simply plug it into ISTA+ or something else? You said you were going to follow up and ask for them to drain the battery, does that mean they didn't initially do so? If you don't mind sharing, did they give you prices for what you'll have to pay for 'testing'? Hopefully they can provide you some additional clarity. Selfishly, I hope they provide you with an answer that provides some clarity for the rest of us as well!

18.8 kWh / 21.6 kWh = 87% of a new battery pack's capacity is usable with 13% being unavailable. This report indicates that 71.23% - 8% = 63% is currently usable, so 87% - 63% = 24% of the new usable capacity is no longer available. The usable capacity loss would need to exceed 30% to trigger a battery pack replacement under warranty.

I think I follow your logic here but it is different than what I was assuming the warranty to be. And no offense to you but I hope you're wrong because my way is more favorable to i3 owners . I may be biased, but I think it actually makes more sense from a usability sense as well but let me know if I'm missing something; since the available capacity of the original battery was 18.8kWh, I assumed the 70% threshold would be 13.16kWh (usable). However, if I'm following your math correctly you're suggesting someone would need to have 57% of the original full battery capacity available to them to hit 30%; BMW gave us 87% of the battery to begin with, subtract 30% and end up with 57%. 57% of 21.6kWh is 12.3. That's a 0.8 kWh difference which isn't a ton but is noticeable when it's ~4% of the total battery.

I'm thinking that taking the usable capacity *.7 is more practical both because it lets BMW do whatever they want with the buffers as long as they can, but also considering this hypothetical: if we make the starting numbers absurd and pretend BMW gave the car a 100kWh pack with 18.8kWh usable, we would only start with 18.8% capacity and it would be impossible to lose 30%. That would either be very clever or very sleazy of BMW.

@gsutiger2 either way, please keep us updated!

 

[eXodus]

My interpretation assuming a 60 Ah battery pack follows.

The full length of the linear bar chart on page 4 of the report shows the full 0% to 100% real charge level range of the battery pack which is greater than the charge level range displayed on the instrument panel due to low and high charge level unavailable capacity buffers. The battery management system (BMS) is limiting the usable charge level range from a minimum real charge level of 8% which is displayed as 0% to a maximum of 71.23% which is displayed as 100%. The top of the black portion of the charge shows the current 91.60% displayed charge level which is a 66.3% real charge level.

The note states that due to battery pack age, the maximum charge level isn't as high as it was when the battery pack was new which reduces the usable capacity. 18.8 kWh / 21.6 kWh = 87% of a new battery pack's capacity is usable with 13% being unavailable. This report indicates that 71.23% - 8% = 63% is currently usable, so 87% - 63% = 24% of the new usable capacity is no longer available. The usable capacity loss would need to exceed 30% to trigger a battery pack replacement under warranty.

If the usable capacity of our battery pack hasn't decreased by more than 30% by the time our battery pack warranty expires, I plan to reset the BMS using ISTA+ to try to increase the usable capacity a bit.

Thanks for the explanation,

Very interesting. I was wondering if the BMS is proportional or a fixed amount.

Further, interesting observation on my 94ah - last week was the first time I almost ran out of range - and put it on the charger with less then 5%, after this my total range increased on every other charge.

So there must be some learning algorithm / reset happening in the BMS, when you draw it all the way down.

For instance, my solar power system BMS need to be calibrated once in a while. For this you need to discharge the battery - all the way - click a button and tell the BMS "this is empty". After this the percentage remaining is more accurate then as from just cycling between 20 and 80%

 

[gsutiger2]

Having 24% of battery gone is not a good sign.

Indeed that is not a good sign if it causes concern for your driving needs. I'm curious: have you done a batt. kapa max reading from the car's service menu? Or a SOH reading from an app like "electrified"? I'm estimating batt kapa max should be somewhere around 13.5kWh?

Also, what did the dealer do to get this report, simply plug it into ISTA+ or something else? You said you were going to follow up and ask for them to drain the battery, does that mean they didn't initially do so? If you don't mind sharing, did they give you prices for what you'll have to pay for 'testing'? Hopefully they can provide you some additional clarity. Selfishly, I hope they provide you with an answer that provides some clarity for the rest of us as well!

18.8 kWh / 21.6 kWh = 87% of a new battery pack's capacity is usable with 13% being unavailable. This report indicates that 71.23% - 8% = 63% is currently usable, so 87% - 63% = 24% of the new usable capacity is no longer available. The usable capacity loss would need to exceed 30% to trigger a battery pack replacement under warranty.

I think I follow your logic here but it is different than what I was assuming the warranty to be. And no offense to you but I hope you're wrong because my way is more favorable to i3 owners . I may be biased, but I think it actually makes more sense from a usability sense as well but let me know if I'm missing something; since the available capacity of the original battery was 18.8kWh, I assumed the 70% threshold would be 13.16kWh (usable). However, if I'm following your math correctly you're suggesting someone would need to have 57% of the original full battery capacity available to them to hit 30%; BMW gave us 87% of the battery to begin with, subtract 30% and end up with 57%. 57% of 21.6kWh is 12.3. That's a 0.8 kWh difference which isn't a ton but is noticeable when it's ~4% of the total battery.

I'm thinking that taking the usable capacity *.7 is more practical both because it lets BMW do whatever they want with the buffers as long as they can, but also considering this hypothetical: if we make the starting numbers absurd and pretend BMW gave the car a 100kWh pack with 18.8kWh usable, we would only start with 18.8% capacity and it would be impossible to lose 30%. That would either be very clever or very sleazy of BMW.

@gsutiger2 either way, please keep us updated!

Yes, BMW is paying for all of this. They did not initially drain the battery even though I told them initially they needed to do this. Of course, I suspect a mechanic with little to no experience with I3's ended up with my car. To insult me further, the mechanic told the service agent to tell me that these batteries do not have problems :shock: . I stopped him right there and told them they need to drain the battery and give me an official battery capacity percentage and state of health.

Today they are expected to drain the battery. However, I think I don't want to deal with this BMW service center. Again, with EV's I find the dealerships look at these cars as though they did not know their company manufactured them (I have a Leaf). Instead of doing the research, they just tell you everything is fine and run any test to get you to go away.

I just wish there was a universal official BMW battery capacity/SOH report that is clear and easy to read with an official mechanic signature. There is no reason for all of this guesswork. I appreciate the Nissan Leaf for being pretty upfront with the capacity bars right on the screen (though this does not show the entire picture). At least you know what you may be dealing with.

Thank you all for your help. More to come!

 

[alohart]

I think I follow your logic here but it is different than what I was assuming the warranty to be. And no offense to you but I hope you're wrong because my way is more favorable to i3 owners . I may be biased, but I think it actually makes more sense from a usability sense as well but let me know if I'm missing something; since the available capacity of the original battery was 18.8kWh, I assumed the 70% threshold would be 13.16kWh (usable). However, if I'm following your math correctly you're suggesting someone would need to have 57% of the original full battery capacity available to them to hit 30%; BMW gave us 87% of the battery to begin with, subtract 30% and end up with 57%. 57% of 21.6kWh is 12.3. That's a 0.8 kWh difference which isn't a ton but is noticeable when it's ~4% of the total battery.

I think you're onto something. When I think of battery pack capacity, I generally think in kWh. However, the bar graph in the report is in percentage of new gross capacity, so I dealt (incorrectly?) with capacity percentages only. However, the 30% capacity loss limit is based on new usable capacity. I think my logical error was:

87% - 63% = 24%

which should have been:

(87% - 63%) / 87% = 28%

If so, gsutiger2's battery pack has lost 28% of its new usable capacity, not 24%. Does this seem correct? If so, I'll edit my original post so others won't be mislead by my mistake.

 

[3pete]

(87% - 63%) / 87% = 28%

If so, gsutiger2's battery pack has lost 28% of its new usable capacity, not 24%.

I think this makes sense. Maybe a different way of stating it that converts to kWh but otherwise calculates the same thing:

71.23% current max allowed - 8% current min allowed = 63.23% current gross batt % left.
63% of the gross battery capacity (21.6 kWh) is 13.6kWh.
13.6kWh / original available battery capacity (18.8 kWh) is ~72% original available capacity left
100 - 28% = 28% lost.

I would also expect gsutiger2's Batt Kapa Max value to be somewhere around 13.6 after a full charge.

Of course, it'd be nice if BMW made this less complicated to measure rather than guessing/estimating at capacity and its relation to the warranty.