Oleksiy
Posts: 45
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: Battery issue

Thu Nov 08, 2018 3:21 pm

I don't know why people are paying attention to this indicator despite being confident that it's useless. I disagree with the latter. I've been compiling daily stats on Batt.Kapa.max, and its (monthly) averages seem to be quite close to the SOH calculated via the trip computer data. I've been following Batt.Ladung as well, and this one is all over the place. It matches Batt.Kapa only at 100% SOC, and in all other cases severely underestimates the current "capacity" of the pack.

My understanding of Batt.Kapa is that it provides some estimate by the BMS of the total kWh amount that was able to sneak into the battery during the latest charging session (the BMS extrapolates in case the charging was stopped before 100% SOC). Then this very amount is being used while driving - no more than this really, if the BMS "thinks" that's the max in there. So, when you approach a depletion of this amount, the BMS signals you with XX range remaining warnings and then shuts down the system. If this hypothesis is true, Batt.Kapa is the true SOH at any given moment. At least the SOH I'd be interested in - 'cos I'd like to use some kWh from the pack to drive, and that's the amount I can use.

Why it varies so much for so many people is another question. From the data I have so far, its variability was quite modest during summer, but then it started falling rapidly with the decrease of ambient temperature (October-November). This makes sense - the battery's capacity decreases in cold conditions. Batt.Kapa may vary also depending on the state of cell balance, and due to the normal (or abnormal) degradation of the pack. Maybe there are other factors at play, I don't know.

Now, this hypothesis may be thrown away based on your case - you have a 12.5 kWh Batt.Kapa and a decent range of 75 miles. In case Batt.Kapa is fair in the assessment of the true capacity of the pack, you efficiency should be about 6 miles/kWh, quite a stretch. So, I don't know :)

Other reported low Batt.Kapa values (both here and on FB group threads) matched well with the GOM based and actual range, so your case is unique and thus very interesting. But if I were in the US, I'd certainly try to talk to the dealer on this basis asking them to assess the pack (they run some procedure, I understand), and replace it under warranty in case it's below 70% (12.5 kWh means it's at 66% SOH, if we were to believe the Batt.Kapa here).
Last edited by Oleksiy on Fri Nov 09, 2018 5:56 am, edited 1 time in total.

Oleksiy
Posts: 45
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: Battery issue

Thu Nov 08, 2018 3:41 pm

One more thing, it's also possible to assess the capacity of the pack by contrasting the amount of kWh that was used to charge the pack (if you have a meter) vs. the calculated number of kWh utilized to propel the car before this charging session. I did this, and worked quite well in summer when the temperature was stable and charging losses were low, abut 5-10%. Now the losses seem to vary a lot from day to day, maybe because the battery is trying to precondition itself and climatize the cabin, I'm not sure. In summer my total kWh used for car charging matched my calculated numbers quite closely. This is one more reason I made the assumptions set out in my previous message.

jadnashuanh
Posts: 4165
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Battery issue

Thu Nov 08, 2018 6:20 pm

In the winter, it may be the 1Kw battery heater that impacts your total input verses what actually goes into the battery that can be used. Especially if you have a REx, in the winter, heating the cabin can take a big cut of your SOC, less so in a BEV, but warming the battery can eat up a fair amount of power.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

jlangham
Posts: 19
Joined: Sun Nov 04, 2018 6:01 pm

Re: Battery issue

Fri Nov 09, 2018 5:17 am

All,
Great replies! I am getting the 70-75 mile range ONLY if I stay in Eco Pro + mode the entire time, which means no highway. My daily commute takes me on a highway for about 2/3 the time so realistically I'm getting a range of 50ish miles with combo of Eco+/Eco (no Comfort). My gauge shows 4.5 mil/kWh is what I'm averaging. My workmate that drives a Leaf said he's getting in the 3s, so I'm still thinking things are ok enough to not worry at this stage. I looked at the Batt. Kappa again this morning when I got to work (60 degrees in garage here in Phoenix) and it showed 12.8 and still have 68% charge after an 18.9 mile one way trip (again, with a mix of Eco+/Eco driving). Does this sound reasonable? It's working for me for now.

Yes, my dealer service manager did respond in email to my questions and said they do have a battery test they can run if I still have questions. I just might do that to finally put to rest this issue.

This is still all new to me and you'd think with me being an Engineer, I'd have it all figured out by now! :D ;)

Oleksiy
Posts: 45
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: Battery issue

Fri Nov 09, 2018 5:55 am

It seems your numbers match well. 18.9 miles on 32% of battery capacity utilized means that your pack's 100% provides for 59 miles. And if we divide this number by 12.8 kWh of Batt.Kapa reading, we arrive at 4.61 miles/kWh efficiency, which is very close to the number you provide (from the trip computer, I assume) - 4.5 miles/kWh.

Given this (albeit limited) set of data, I'd say the current capacity of your pack is about 12.5-13 kWh, or 66-69%. In case it's the real thing, and not due to the unbalanced cells (you could easily correct this by charging the car up to 100% and leaving it for some time in this state for several days in a row), or alternatively due to the accumulated BMS errors (could be corrected via battery re-initialization), you pack should be eligible for the replacement under warranty.

These are all my guesses, your dealer will have a say on this.

jlangham
Posts: 19
Joined: Sun Nov 04, 2018 6:01 pm

Re: Battery issue

Fri Nov 09, 2018 6:26 am

Oleksiy wrote:It seems your numbers match well. 18.9 miles on 32% of battery capacity utilized means that your pack's 100% provides for 59 miles. And if we divide this number by 12.8 kWh of Batt.Kapa reading, we arrive at 4.61 miles/kWh efficiency, which is very close to the number you provide (from the trip computer, I assume) - 4.5 miles/kWh.

Given this (albeit limited) set of data, I'd say the current capacity of your pack is about 12.5-13 kWh, or 66-69%. In case it's the real thing, and not due to the unbalanced cells (you could easily correct this by charging the car up to 100% and leaving it for some time in this state for several days in a row), or alternatively due to the accumulated BMS errors (could be corrected via battery re-initialization), you pack should be eligible for the replacement under warranty.

These are all my guesses, your dealer will have a say on this.


Thanks Oleksiy for that. I will leave the car on my level 1 charger this entire weekend to see if it does balance it out some.

Looks like I'm going to have to take a trip to the dealer after all then. I'll probably call BMW USA first because, right now, it looks like the dealer is saying, "If your range isn't affected, then you're fine." And I'm getting good range, but that doesn't mean the battery is good. They said they would hook up the car to their tester and verify, so I guess that's what I'm going to have to do.

So my workmate suggested I drive the car for about a year more to get the most I can out of this battery, and then replace it under warranty. That way, since I'll only get one battery under warranty, I'll get the longest life out of the car with the new battery.

My quesiton is, does anyone see any problem with, let's say, running the battery to 50-60% battery? Besides maybe taking a range and charging time hit, anything else? As long as there aren't any serious consequences to doing this, it could be an option.

Oleksiy
Posts: 45
Joined: Fri Mar 23, 2018 4:30 am
Location: Kyiv, Ukraine

Re: Battery issue

Fri Nov 09, 2018 7:21 am

Seems like a sensible thing to do, I don't think there any other issues with using a 60% or something SOH battery other than limited range. Check out Leaf forums out there (like https://www.mynissanleaf.com/) - Leaf owners have plenty of experience with deteriorated batteries.

jlangham
Posts: 19
Joined: Sun Nov 04, 2018 6:01 pm

Re: Battery issue

Fri Nov 09, 2018 7:37 am

Yeah, and once I'm clear of the BMW CPO warranties, I wouldn't mind getting the software and coding, battery re-initialization (from the German posts you provided), etc. For now, I'm depending on the dealer and BMW to come through for me. They're not going to pro-actively change the battery from what I'm getting from them, but I'll push them if I have to.

I will continue to watch the Batt. Kappa closely to see if it goes drastically either way - higher or lower. For now, I'll just drive it until the wheels come off! :P

Thanks again.

i3Houston
Posts: 112
Joined: Thu Jul 12, 2018 2:30 pm

Re: Battery issue

Fri Nov 09, 2018 9:02 am

jlangham wrote:All,
Great replies! I am getting the 70-75 mile range ONLY if I stay in Eco Pro + mode the entire time, which means no highway. My daily commute takes me on a highway for about 2/3 the time so realistically I'm getting a range of 50ish miles with combo of Eco+/Eco (no Comfort). My gauge shows 4.5 mil/kWh is what I'm averaging. My workmate that drives a Leaf said he's getting in the 3s, so I'm still thinking things are ok enough to not worry at this stage. I looked at the Batt. Kappa again this morning when I got to work (60 degrees in garage here in Phoenix) and it showed 12.8 and still have 68% charge after an 18.9 mile one way trip (again, with a mix of Eco+/Eco driving). Does this sound reasonable? It's working for me for now.

Yes, my dealer service manager did respond in email to my questions and said they do have a battery test they can run if I still have questions. I just might do that to finally put to rest this issue.

This is still all new to me and you'd think with me being an Engineer, I'd have it all figured out by now! :D ;)


To determine the range, its best to drive the car at constant speed and then compare the range with what EPA has set, which is 72 miles for mixed city and freeway driving.

I have a 2015 Rex, with about 20K miles, driving it on freeway(95% of the time) at speeds between 65-75 mph, I get about 60 miles of range. AC is set to 70F in M mode.
TM3 Reservation holder/ 2015 i3 Rex

jlangham
Posts: 19
Joined: Sun Nov 04, 2018 6:01 pm

Re: Battery issue

Fri Nov 09, 2018 12:21 pm

i3Houston wrote:
jlangham wrote:All,
Great replies! I am getting the 70-75 mile range ONLY if I stay in Eco Pro + mode the entire time, which means no highway. My daily commute takes me on a highway for about 2/3 the time so realistically I'm getting a range of 50ish miles with combo of Eco+/Eco (no Comfort). My gauge shows 4.5 mil/kWh is what I'm averaging. My workmate that drives a Leaf said he's getting in the 3s, so I'm still thinking things are ok enough to not worry at this stage. I looked at the Batt. Kappa again this morning when I got to work (60 degrees in garage here in Phoenix) and it showed 12.8 and still have 68% charge after an 18.9 mile one way trip (again, with a mix of Eco+/Eco driving). Does this sound reasonable? It's working for me for now.

Yes, my dealer service manager did respond in email to my questions and said they do have a battery test they can run if I still have questions. I just might do that to finally put to rest this issue.

This is still all new to me and you'd think with me being an Engineer, I'd have it all figured out by now! :D ;)


To determine the range, its best to drive the car at constant speed and then compare the range with what EPA has set, which is 72 miles for mixed city and freeway driving.

I have a 2015 Rex, with about 20K miles, driving it on freeway(95% of the time) at speeds between 65-75 mph, I get about 60 miles of range. AC is set to 70F in M mode.


Actually, I get less driving it only on the highway than I would in the city, which is what I'm seeing. Because of regenerative braking, I get much better range than on the highway even at constant speed. When I am on the highway, I just set the cruise control and I'm good, but range is much less than puttering around town from Wal-mart to Costco, etc.

If I only drove highway, and only in Eco Pro mode (only 75 mph tops), I believe I would barely get 50-55 miles. That's what I'm getting right now, with this battery. That's why I hope the battery does drop off enough soon so the dealer will replace it.

Return to “News and Main BMW i3 Forum Discussions”