sogorman
Posts: 9
Joined: Sat Jul 07, 2018 1:00 pm

2015 i3 Battery Degradation (20% after 30k miles)

Sat Jul 07, 2018 1:13 pm

Long time lurker, first time poster.

Last week, I picked up a 2015 i3 with 33k miles on the ODO here in Phoenix. I have a 2015 Model S (which is soon to be sold and a 3 in it's place) that my wife and I share and I wanted an EV for my daily commuter into work. I love the interior of the i3 and while I have never owned a BMW I am a fan of their engineering. My comute is 49 miles round trip and I figured that even with a used i3 with 10% battery degradation (side note my tesla has 4% degradation after 68,000 miles) and with the over estimated EPA range I would have more then enough range to get me to work and back home every day.

Friday was the first attempt at the 49 mile round trip commute and i made it home with only about 5 miles left on the ODO.... not what I was hoping for. Today I decided to do a range test going from 100% SOC down to near 0%, recording the consumption and range and then calculate the used kWh and determine how much degradation this i3 with 33,000 miles had on it from the original usable 18.8 kWh. Using the tools at my disposal, it looks like my i3's battery has degrated about 21% and is now sitting at or near 14.84 usable kWh.

Here is a spreadsheet with my calculations.. I plan on attempting this experiment every 45 days or so and see how the battery is doing.

https://docs.google.com/spreadsheets/d/ ... sp=sharing

I love the car but 20% battery degradation seems a bit extreme, part of me hopes that it gets up to 30% so I can deal with BMW but the other part of me wishes I could have a car with more range than ~54 miles.

Any thoughts?
Last edited by sogorman on Sat Jul 07, 2018 2:11 pm, edited 1 time in total.

theothertom
Posts: 364
Joined: Mon Mar 20, 2017 6:08 am
Location: South Carolina

Re: 2015 i3 Battery Degradation

Sat Jul 07, 2018 1:43 pm

You can check the battery capacity in the hidden menu. Search the internet using your favorite search engine for batt.kap.max. Here's one link from this forum
viewtopic.php?t=2793

I recall one post, maybe on this forum or perhaps the Facebook group, where the capacity dropped below 70% and BMW replaced the battery. I assume your car is still under warranty....you might want to get the dealer to check the battery...perhaps they can tell if it has a bad cell or something.
Others can comment if ~54 miles is normal for a 2015 BEV, but of course it will depend on driving conditions and driving style.

sogorman
Posts: 9
Joined: Sat Jul 07, 2018 1:00 pm

Re: 2015 i3 Battery Degradation

Sat Jul 07, 2018 2:00 pm

Thanks @theothertom. The Max. Kappa. kWh secret menu is an estimation from the BMS. My reads 14.8 which is inline with my actual measurement. You are correct about the 100k 70% warranty, I guess I am just a bit disappointed at almost 20% capacity / range loss at only 33k miles.

alohart
Posts: 2125
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sat Jul 07, 2018 3:13 pm

If your i3 has spent its entire life in Phoenix, its battery pack could have been hot long enough to increase the battery cell degradation rate. Unlike a Tesla Model S and probably Model 3, the i3's battery pack cooling system does not automatically operate when an i3 is parked, so an i3 parked in the sun on hot pavement or in a hot garage won't automatically keeps its battery pack cool. If battery pack preconditioning is on, cooling would operate only long enough to cool the battery pack immediately before a set departure time which would not keep the battery pack cool at all times. This might require an EVSE to be plugged in as well, but those more familiar with battery pack preconditioning will correct what I've written if it is incorrect.

So it's possible that significant irreversible battery cell degradation has occurred, especially if the previous owner always charged the battery pack to an indicated 100% (an actual 90-93%) and allowed it to remain full for extended periods of time during hot conditions.

If you're lucky, the previous owner may have rarely charged to full such that the accelerated cell self-discharge rate at higher temperatures has resulted in the charge levels of the cells varying considerably (a.k.a., cell imbalance). Unfortunately, cell balancing occurs most rapidly when the battery pack is left at full charge for an extended period, the very conditions that result in an increased permanent cell degradation rate.

If our battery pack seemed to have a low capacity and I knew that it had not had much opportunity for cell balancing (i.e., it had not remained at full charge for an extended period of time), I would try charging it to full and leaving the EVSE plugged in to keep the charge level full as cell balancing decreases the pack's charge level, all under cool conditions, if possible.
Aloha,
Art

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

jadnashuanh
Posts: 5037
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sat Jul 07, 2018 3:34 pm

FWIW, once the battery is fully charged, other than some cell balancing that might occur after that, it could be a number of days before the SOC dropped enough to cause the i3 to turn the EVSE back on. After 4-years, mine seems to provide about the same max range, and I almost always just plug in when I get home, and unplug only just before I leave. I try to set a departure time when it's not a spur of the moment event, whether it's summer or winter. Mine sits outside where the temperature can vary between about -15 to over 100F, depending on the season. WHen it's hot, I do try to put the car cover on it that tends to limit the heat buildup, at least to ambient or so.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above

sogorman
Posts: 9
Joined: Sat Jul 07, 2018 1:00 pm

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sat Jul 07, 2018 7:33 pm

@alohart, yes I know that the Tesla's (S,X,3) not only use active cooling in the case of the i3 but also passive cooling (i.e. the car is 'turned off' and sitting in the parking lot the car will keep the pack temp within specs). I doubt that the pack is just out of balance... I don't see how 20% range loss can be accounted to cell imbalance. Unfortunately I think my best best is to keep her parked in the sun until it hits 30% loss at which time talk to BMW

@jadnashuanh you are correct, once the SOC reaches 100% and even when balancing needs to occur the car will signal to the EVSE to open the contractors which disconnects the car from the charger. The BMS units will then balance the cells with the car disconnected and then once the overall pack SOC reaches a lower threshold will signal the EVSE to close the contractors to begin charging again.

Oleksiy
Posts: 93
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sun Jul 08, 2018 11:05 am

Cell imbalance may be the culprit as well. I’m not sure how the i3 BMS works, but in Leafs the range estimate and other metrics are said to be calculated by the lowest voltage cell and reported on this basis. Once this cell (or range of cells) is balanced with the others, the reported capacity my increase dramatically in case if a significant difference before balancing. Try leaving the car plugged in after reaching 100% for some days to check this assumption.
Last edited by Oleksiy on Mon Sep 03, 2018 10:39 pm, edited 1 time in total.

arodi3
Posts: 22
Joined: Thu Apr 26, 2018 10:21 am

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sun Jul 08, 2018 11:26 am

My 2015 i3 REX does run its compressor when parked (presumably to cool the battery), but only when plugged in. During summers in Austin, I hear the compressor running quite a bit, even when the car is parked under a carport. Also, after a drive on a hot day, my car often runs the compressor for a while after I park it and plug it in. I have not noticed much degradation, but I could see that maybe if the previous owner left the car unplugged in the heat a lot, it could have damaged the battery.

It would be nice if BMW would let us set different battery schemes to optimize for reduced battery degradation, or for increased range. I could also see having the app alert drivers when the car is parked and the battery is heating up too much, so that the driver could make the call about turning on active cooling at the expense of some range.

alohart
Posts: 2125
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sun Jul 08, 2018 11:58 am

arodi3 wrote:My 2015 i3 REX does run its compressor when parked (presumably to cool the battery), but only when plugged in.
Have you noticed whether the A/C compressor continues running after the battery pack is fully charged? My sense is that the A/C compressor, DC-DC converter charging the 12 V battery, and the high-voltage system in general shut off after the battery pack is fully charged even though an EVSE is still plugged in. However, I might certainly be incorrect.
Aloha,
Art

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

sogorman
Posts: 9
Joined: Sat Jul 07, 2018 1:00 pm

Re: 2015 i3 Battery Degradation (20% after 30k miles)

Sun Jul 08, 2018 2:17 pm

@Oleksiy I am sure the cells are not imbalanced, I have had the car at fully charged connected to a L2 for two days before running the first test in my google doc.

https://docs.google.com/spreadsheets/d/ ... sp=sharing


@alohart and @arodi3 Yes the car will attempt to cool and regulate the HV pack temperature when plugged into L2 even at 100% SOC. Sometimes I can catch both my model S and now the i3 with the cooling fans on even at 6:00am when they have been in a shaded garage overnight. Note that the temperature in the garage is around 100F when this happens. This indicates that the i3 would like to have it's cells under 100F. Now, if we park the i3 in the phoenix sun where today it's 110F out and a car parked in the sun the interior will easily reach 140F (and eventually the HV pack as well) I hate to think what is happening to the cells. My Tesla will run the fan and even the compressor to attempt to keep the cells at a healthy temp.

I really can't decide whether to further push the cells into an unhealthy state and trigger the 30% warranty or try and baby it.

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