Battery capacity issue

[Oleksiy]

It is true that there is no instantaneous way to measure a capacity of any battery pack (many different capacities exist depending on conditions). So it would be difficult to provide an i3 driver with a definitive pack capacity.

This is a very fair point. It is sad though, that it's true for BMW that there is no instantaneous way to measure a capacity of the battery pack. It is not necessarily true for other brands though. E.g., Nissan LeafSpy provides a very accurate estimate of battery capacity at any moment, and this estimate closely matches the dashboard battery capacity indicator in bars, the latter triggering a battery warranty whenever there's less than 9 bars remaining. All these also match the outcome of battery capacity assessment using more rigorous tests via slow discharging and charging of the battery. And Leaf has had this capability from the onset, it's not that BMW had to invent a wheel.

I doubt BMW don't have algorithms to estimate the battery capacity by voltage range etc. at any given moment, since Nissan has used them since 2011. I just think it's a lot more convenient for BMW to communicate they don't. And to obscure the process of battery capacity verification and its outcomes in every possible way.

 

[Anonymous]

Interesting article by an i3 owner, and the formula he uses to track his battery capacity, since both the GOM range and the battery kappa/max aren't reliable measures.

https://www.bmwblog.com/2017/04/24/bmw-i3-long-term-battery-capacity-report-better-expected/

Since BMW claims the car will alert them when the battery capacity drops below 70%, they should not have a problem letting owners know what that trigger actually is.

I suspect it isn't a hidden "number" that can be constantly monitored. More likely something built-in to the battery management system, for example. when cell balancing to or above a set parameter fails.

 

[vinc]

I find very interesting that there isn’t a single member who can share a first hand experience of having the battery replaced under warranty. If you go to a Tesla forum, for instance, you quickly hear from people who did.

It certainly does sound like BMW really, really, really doesn’t want to replace the battery. Or the i3 is unusually reliable, which might be true all jokes aside.

 

[Oleksiy]

Interesting article by an i3 owner, and the formula he uses to track his battery capacity, since both the GOM range and the battery kappa/max aren't reliable measures.
https://www.bmwblog.com/2017/04/24/bmw-i3-long-term-battery-capacity-report-better-expected/

I've been tracking estimated SOH both using a similar formula (I use efficiency and miles driven to get kWh used for the trip, and then divide this number by depth of discharge to obtain SOH) and a Batt.Kapa reading. They are more or less close in terms of monthly averages - summer SOH is 0.1-0.4 kWh higher for calculated values and Batt.Kapa outcomes are higher in winter (they converge in moderately cool weather in Sep and Oct):

month * calculated SOH, kWh * Batt.Kapa SOH, kWh
May-18 * 18.2 * 18.1
Jun-18 * 18.6 * 18.1
Jul-18 * 18.1 * 18.0
Aug-18 * 18.0 * 17.9
Sep-18 * 17.8 * 17.8
Oct-18 * 17.6 * 17.6
Nov-18 * 17.2 * 17.5
Dec-18 * 16.9 * 17.4
Jan-19 * 16.7 * 17.2

I also contrast these with Batt.Ladung reading - this is the remainder of kWh in the battery at any given time. One could calculate battery's full capacity if this number is divided by SOC %. This one is not even close. When at or around 100% SOC, it matches Batt.Kapa.max, and at lower SOC it severely underestimates the capacity of the pack. E.g., my winter average estimated SOH using this metric is 15.3 kWh or 81% (I usually take readings in the end of the day at lower SOC).

As far as I understand (I read this in many places), Batt.Kapa.max is calculated on the basis of the amount of kWh that sneaked into the battery during the last charging session. It corresponds with my observations - the number very rarely fluctuates between charges, but often shifts to some new value immediately following a new charging session. Should this assumption be correct, I would use Batt.Kapa as the true indicator of battery health, since the capacity of a bottle is the volume of liquid you could pour into it.

Now, to avoid extrapolation errors, it's best to discharge the battery to zero (this would mean 8% of the true battery SOC), and then charge it to 100% SOC (94% true SOC of a healthy battery) and read Batt.Kapa.max. In this case the indicator will represent the most correct SOH possible, I assume. Well, unless the BMS messes things up due to some reason, actively precluding the battery to be filled up to its full.

 

[JLB2]

My home charger (Chargepoint) gives me the amount of KWH's that was transferred to my i3 during a charging session. Starting at an indicated range of 5 miles, Chargepoint said that about 15.5 kwh's were required to charge my car to 100%. That about matches what kappa.max indicates. I suppose 2nd source of data is a good validation of BMW's number.

We are all experiencing degradation to one extent or another. Degradation happens at an increasing rate so I expect more and more i3's will start to hit kappa.max of 12kwh's or less in the next 2 years. The 2013's and 2014's will be 8 and 7 years old at that point, still within the warranty period.

It would be helpful to all if we continue to report degradation issues and BMW responses. I only hope BMW doesn't stiff us out of a warranty replacement.

If anyone learns of a battery replacement under warranty, please do share it here.

 

[jadnashuanh]

From an engineering teardown (Munroe sp?) they indicated that BMW chose a higher cost, longer lived battery chemistry versus that used in the Tesla...time will tell. Now, whether that is also true on the subsequent capacity increases, I don't know, as the analysis was done on the original battery chemistry/configuration.

 

[alohart]

My home charger (Chargepoint) gives me the amount of KWH's that was transferred to my i3 during a charging session.

That's not the energy actually used to charge the battery pack due to some of the energy being converted to waste heat during charging. The Idaho National Labs measured a 2014 i3's charging efficiency at various charging powers. The most efficient charging, 93%, was 30 A @ 240 V. Lower charging powers were less efficient.

Whereas, Batt. Kapa. max is the calculated maximum energy that could be added to the battery pack (i.e., excluding wasted energy).

So to make these equivalent, you'd need to correct the Chargepoint energy for energy lost to heat (i.e., at least 7% less than Chargepoint reports).

 

[jadnashuanh]

And, depending on the ambient conditions, some of that power could easily be used to condition the battery (heat or cool) and not actually get stored in the battery.

 

[JLB2]

Good points regarding Chargepoint. This further proves that my battery is degrading faster. My 2014 i3 is now 5 years old with about 48k miles driven. That's about 80% of original capacity. It degraded by about 5% per year in the last 3 years. In 2 years, it'll probably be down to 70%. I just hope BMW honors the warranty.

I wonder what they will do in 2023 when the 2014's are out of warranty and need new batteries. I'm sure many of the cars will still be functioning perfectly but needing new batteries. Will they allow owners to buy battery replacements?

 

[TheMK]

I wonder what they will do in 2023 when the 2014's are out of warranty and need new batteries. I'm sure many of the cars will still be functioning perfectly but needing new batteries. Will they allow owners to buy battery replacements?

Hopefully they'll let you do a swap for a nice price, though I'm sure "nice price" will be $5000. Perhaps they will let you buy the newer 94Ah and 120Ah battery packs used in the 2017+, and 2019+ respectively. All jokes aside, I'm not sure if I will still be in my '14 in 2023, I'd like to get a '19 i3 sport BEV, or maybe a used Tesla depending on cost of ownership (Tesla has ridiculously high out of warranty costs). A lot of it comes down to how rapidly 2019 models depreciate.

 

[alohart]

I wonder what they will do in 2023 when the 2014's are out of warranty and need new batteries. I'm sure many of the cars will still be functioning perfectly but needing new batteries. Will they allow owners to buy battery replacements?

Based on the experience of gasoline-electric hybrids with bad battery packs, 3rd-party battery pack builders offer replacement packs for considerably less than the car dealer's retail price. Battery cell quality would be my main concern. However, there's no reason why a 3rd-party battery pack builder would not be able to buy the same cells used by the car manufacturer. As EV battery pack warranties begin to expire, I expect choices to become available.

 

[jadnashuanh]

On a commercial basis, BMW has been retasking replaced battery packs as backup systems. I saw one prototype designed for use in a home they showed in a press release as a possibility, but I've not seen that they ended up offering for sale anywhere. At least the engineering has been done. There is expected to still be a very significant capacity left in a battery pack once it is deemed less than ideal in a vehicle. Personally, I would like the idea...there'd still be enough power to get through probably a couple of days with power out if you conserved some. And if you were really conservative, a lot longer.

What I've heard on the rebuilders is that they disassemble used packs, discard modules that are less than satisfactory, and reassemble from the good ones. The i3 was designed with fairly large cells in easily replaced modules (well, easier than most), so replacing a bad module is likely to be the first line of attack. IMHO, thousands of small cells, like in the Tesla offers more chances of failure than the barely 100 in the i3. The fewer internal and external connections there are , the more reliable it should be.

Seems the battery degradation thing peaks this time of year as the temperatures drop, while once it warms up, people seem to realize their range is going back up again and relent.

 

[Oleksiy]

We have a huge fleet of used Leafs from the US in Ukraine, a lot of 2011-2013 MY ones as well. Most of these cars have either dead or almost dead packs, quickly approaching or in some cases going below 60% SOH. There's also a burgeoning cell repackaging industry here catering to the needs of these Leaf owners. People can do lots of things. They can easily upgrade 24 kWh packs to newer 30 kWh ones, there have been tries to move to 40 kWh packs as well, although with limited success yet. They install dual batteries, additional packs from Chevrolet Volts and other things. They have developed custom BMS operating systems for Leafs, or rather OS skins providing for a lot of added flexibility, etc.

But, there have been no third party battery pack solutions yet. Also, partial replacement of cells in degraded battery packs proved to be quite a futile exercise. Once done, the packs seem to quickly re-group themselves to degrade a lot faster than previously, and all of a sudden you get the same pack as before but for more money. So, what people do now, they try to replace full packs for the ones taken from salvage cars. This is one of the reasons there's a growing import of wrecked Leafs imported to Ukraine as well.

I follow the Leaf "industry" closely. They are far ahead of BMW in all departments here in terms of serviceability, including the existence of LeafSpy. If the degradation of my i3 's pack going forward is linear, I may see maybe one or two more years in my car until it becomes unusable in winter, so I need to start considering my options today. The most likely one - I'll need to sell the car at a very significant loss (despite my previous thoughts that the notorious EV depreciation had already been captured by the previous owner of the car - I did buy it for 1/3rd of the initial price, a 2.5 year old vehicle in an excellent condition with 15K miles on it).

 

[Oleksiy]

My home charger (Chargepoint) gives me the amount of KWH's that was transferred to my i3 during a charging session.

That's not the energy actually used to charge the battery pack due to some of the energy being converted to waste heat during charging. The Idaho National Labs measured a 2014 i3's charging efficiency at various charging powers. The most efficient charging, 93%, was 30 A @ 240 V. Lower charging powers were less efficient.

Whereas, Batt. Kapa. max is the calculated maximum energy that could be added to the battery pack (i.e., excluding wasted energy).

So to make these equivalent, you'd need to correct the Chargepoint energy for energy lost to heat (i.e., at least 7% less than Chargepoint reports).

Just an observation: had to charge at a public charging station today, paid for 9.7 kWh. I took readouts of Batt.Ladung from the hidden menu before and after the session to measure charging losses:
Before: 19% SOC, Batt.Ladung 3.1 kWh (implied battery capacity = 16.3 kWh), Batt.Kapa 16.9 kWh, ambient temperature +1.5C / 35F
After: 69.5% SOC, Batt.Ladung 12.8 kWh (implied battery capacity = 18.4 kWh), Batt.Kapa 17.0 kWh, ambient temperature +1.5C / 35F

Seems the session was effectively lossless - 9,7 kWh metered - 9.7 kWh added to Batt.Ladung. Also, the post-session implied battery capacity didn't translate into significantly higher Batt.Kapa value, as I would have expected. And, if we divide 9.7 kWh by the depth of charge (9.7 / 50.5%), we get one more implied battery capacity value, this time 19.2 kWh. Go wonder...

(for those, who may be interested, the screenshots are under this link: https://www.drive2.ru/l/524031640918296811/).

 

[jadnashuanh]

One thing that can affect battery life is how well the logic and hardware can handle cell balancing. From what I've read, I think that BMW uses a more sophisticated routine to try to keep the batteries in shape. Leafs also seem deficient in their heat management. Lots of owners in the US southwest had early Leaf battery pack issues. THey still don't do refrigerated cooling...air cooling only (except maybe the newest models?). FWIW, the newest Leafs specify a limit on a single trip of DC fast charges you can do...they can't handle the heat. I do not know if they can preheat the batteries, which helps things in the winter.

 

[metaflash]

I almost have the same problem but thanks guys, I'm reading it all the ideas and suggestions, again thanks

 

[rcyyan]

For everyone in CA, CT, ME, MD, MA, NJ ,NY,RI and VT....I'm guessing we have 10yrs and 150k mi. Or am I reading this incorrectly.

From the owners manual under the emissions warranty section:

Manufacturer’s Warranty Coverage
(California, Connecticut, Maine,
Maryland, Massachusetts, New
Jersey, New York, Rhode Island, or
Vermont ONLY):
– For 15 years or 150,000 miles, whichever
occurs first**:
**Except High-Voltage Battery (Traction Battery),
which is covered for 10 years, or 150,000 miles,
whichever occurs first.

 

[georgd84]

Hello
I have just bought a second hand 2016 reg Rex and I am new to EV's.
Can I ask your views on the Batt kapa max reading on my car which is currently showing 29.2 KWh.
I am confused as I thought the usable capacity is 27.2. Is it possible that the max shown would have been 33 when it was new?

I charge it using a 13 amp domestic socket about twice a week and usually allow it to be below 50 percent when doing so.

Grateful for any help and hope this is posted in the correct place.

David

 

[EvanstonI3]

Hello
I have just bought a second hand 2016 reg Rex and I am new to EV's.
Can I ask your views on the Batt kapa max reading on my car which is currently showing 29.2 KWh.
I am confused as I thought the usable capacity is 27.2. Is it possible that the max shown would have been 33 when it was new?

My view having the same battery with 29.6 KWh showing is this:
The TOTAL capacity of the battery pack is 33KWh.
BMW will not allow the user to use the entire 33, so it holds back around 10% leaving around 30KWh. That's what it perhaps showed when new. (or at least something very close).
BMW advertises a "useable capacity" of 27.2 but I think this is deliberately de-rated for warranty purposes. I am guessing that number is what they will base future battery warranty claims on, not 33KWh or 30KWh.

 

[georgd84]

Thanks for your help. So it looks like neither of us need to worry about our battery capacities at the moment.
David