Battery range dropping fast

[Whereitis]

I bought a 2014 i3 Rex last summer with 55k miles on it. When I first got it, it would show 60 miles available on a full (overnight) charge. A couple of months later it started showing 55 miles. Now it's 5 months later, I go out to the car and it shows 47 miles with a full charge. The car only has about 58k on it now. Has anyone seen the HV battery lose its capacity so fast? I'm concerned this means the battery is about to die.

 

[mojo]

Assuming you're in the Northern hemisphere, it's approaching the coldest time of year. It's normal to see the range drop in winter. ~20% is typical but (of course) varies depending on the temperature conditions where you are.

 

[Whereitis]

Assuming you're in the Northern hemisphere, it's approaching the coldest time of year. It's normal to see the range drop in winter. ~20% is typical but (of course) varies depending on the temperature conditions where you are.

Well, it's gone from 70s and 80s down to 40s and 50s, so I suppose that could be it. I hope it doesn't drop much further when temps get down to below freezing.

 

[mojo]

There are other factors - one being the difference in driving style between you and the previous owner. If (for example) the previous owner only travelled slowly on city roads and you use high-speed roads, the guessometer would take a while to adapt to the new "normal", so you would expect that to correct after the first few drives in your ownership - it would not be immediate - though I concede that the process should take a matter of days or weeks - not months!

 

[Whereitis]

There are other factors - one being the difference in driving style between you and the previous owner. If (for example) the previous owner only travelled slowly on city roads and you use high-speed roads, the guessometer would take a while to adapt to the new "normal", so you would expect that to correct after the first few drives in your ownership - it would not be immediate - though I concede that the process should take a matter of days or weeks - not months!

That was my thought too. But after a few occasional reads of 60 when I first got the i3, it's mostly shown consistently in the 55-57 mile range when reading "100%" in the HSOC screen. Now it still says 100%, but with miles showing 47. This readout change seems to have happened just within the last few days, not months or even weeks. I hope it never reaches zero - the car might never start again lol

 

[Joff]

45 miles range is pretty low. As has been mentioned, temperature is a big factor. Another lesser known factor is that if you don't run the battery all the way down once in a while, the car's estimation of it's battery capacity can become less accurate, usually tilting toward the safe side, reporting less.

 

[Whereitis]

45 miles range is pretty low. As has been mentioned, temperature is a big factor. Another lesser known factor is that if you don't run the battery all the way down once in a while, the car's estimation of it's battery capacity can become less accurate, usually tilting toward the safe side, reporting less.

I didn't know that. It may be the reason, since in the past few days I only ran the battery down to half before reaching home and plugging back in

 

[jfran2]

FWIW, I don't think your readings are unusual. I have a 2015 Rex with 87,000 miles, and I only occasionally see 60 miles anymore on a full charge. Usually my mileage is in the mid 50's with wintertime dipping into the upper 40's. That's consistent with the 2% per year degradation I hear talked about with this particular battery pack. I don't worry about mine; I'm thankful to have the get-out-of-jail-free card of the Rex in the back!

 

[Whereitis]

FWIW, I don't think your readings are unusual. I have a 2015 Rex with 87,000 miles, and I only occasionally see 60 miles anymore on a full charge. Usually my mileage is in the mid 50's with wintertime dipping into the upper 40's. That's consistent with the 2% per year degradation I hear talked about with this particular battery pack. I don't worry about mine; I'm thankful to have the get-out-of-jail-free card of the Rex in the back!

That's also why I bought a Rex and would not buy a full electric anything until the charging infrastructure is much improved.

 

[Gonville]

Well, it's gone from 70s and 80s down to 40s and 50s, so I suppose that could be it. I hope it doesn't drop much further when temps get down to below freezing.

It will - check the graph. (Data from US Government test labs reference in the picture)

Bad things happen below zero. Pre-condition. Oh and ABC

 

[Gonville]

45 miles range is pretty low. As has been mentioned, temperature is a big factor. Another lesser known factor is that if you don't run the battery all the way down once in a while, the car's estimation of it's battery capacity can become less accurate, usually tilting toward the safe side, reporting less.

And conversely if you don’t charge it to full there is no cell balancing which will reduce capacity just as surely. Have a look at this picture. As a result of not charging beyond 80% - bad advice.

(Fully recovered to 70+ miles after 3 months of leaving it plugged in after every trip)

 

[Mondomensch]

And conversely if you don’t charge it to full there is no cell balancing which will reduce capacity just as surely. Have a look at this picture. As a result of not charging beyond 80% - bad advice.

(Fully recovered to 70+ miles after 3 months of leaving it plugged in after every trip)

Any idea how close to 100% is needed to get the cell balancing activated?

 

[alohart]

Any idea how close to 100% is needed to get the cell balancing activated?

In September, 2016, British i3 owner Bev Brown was given a workshop tour of the BMW UK HQ where a BMW employee, "The Professor", explained i3 battery cell charge level balancing. "The Professor" said that the charge level "just needs to be above 80% to get the in-car cell balancing active." Cell balancing occurs when the HV system is sleeping (i.e., when the HV battery pack isn't connected to the HV circuit, so not while driving or charging). "It doesn’t matter if you regularly do small top up charges to 60% or not. The very clever BMW Battery Management System (BMS) takes care of it all for you, just so long as you let it have a [80%+] charge regularly" and then "let it have a long, restorative sleep." It's not necessary to leave an EVSE plugged in.

That's been my experience over 10 years of i3 ownership during which I routinely charged our i3's to a displayed 80%-90% charge level unless I might need full range soon. Occasionally displaying BMS data with the mi3 app showed that the minimum and maximum voltages of all 96 battery cells were always within 0.01V at a full charge indicating excellent charge level balance even without routinely charging to 100%.

 

[Gonville]

Any idea how close to 100% is needed to get the cell balancing activated?

This is huge matter of debate with no concrete evidence - but - what the professor at BMW HQ told us - details in the David Bracknell book complete with photographs - is that cell balancing happens “when charging is complete”. The current view was that certainly at 100% but some views that it happens when unplugged if the charge is above 85%.

 

[Whereitis]

I typically leave the car plugged in overnight using my home charger, and if I don't use the car on a given day it stays plugged in. It seems to me that it will usually be charged to 100% and stay that way until unplugged as I prepare to drive it. Why would you ever let it only get to 80-90% if you won't be using the car at that moment? Isn't it easier to just leave it plugged in all the time?

 

[alohart]

Why would you ever let it only get to 80-90% if you won't be using the car at that moment? Isn't it easier to just leave it plugged in all the time?

Lithium ion battery cells degrade more rapidly at higher charge levels. Some of us plan to keep our i3's until a repair occurs that is so expensive that it's not worth doing. Reducing the odds of the battery pack degrading so much that the reduced range becomes a problem before the expensive repair happens is a no-brainer. Some argue that an i3 at a displayed 100% charge level really isn't at the highest possible charge level due to the buffer that the BMS implements, so there's no problem. A displayed 100% charge level is an actual charge level of >90%, probably closer to 95%. The cell degradation rate at even a 90% charge level is greater than that at a 80% charge level. Is this enough to matter? Who knows, but why take a chance?

With that in mind, why would anyone always charge to 100% unless the full range might be needed soon, especially allowing the battery pack to remain at a full charge for hours?

We are advised to disconnect appliances that always consume electricity, so why would anyone leave an EVSE on at all times when it is doing nothing useful a high percentage of the time? An EVSE plugged into an EV after the EV is fully charged does nothing but waste electrical energy. In addition, a power surge could damage an EVSE that's always on or even possibly the charger in an EV when an EVSE is plugged in. So why leave an EVSE plugged into an EV any longer than necessary?

How hard is it to unplug an EVSE when the desired charge level is reached? I turn on the power to our EVSE, plug it in to our i3, look at the estimated charge completion time on the instrument panel, and set an alarm on my watch for 1 hour earlier which corresponds to ~85% with our i3 and EVSE. When the alarm goes off, I unplug our EVSE and turn off its power. Easy-peasy…

 

[Mondomensch]

How hard is it to unplug an EVSE when the desired charge level is reached?

I think this still varies a lot as we adjust to car charging. I haven't yet set up for charging at home, so charge at public chargers. Depending on the charger and company, it can be tricky to set a final charge level in advance, and manually checking to stop remotely via charging company app can be annoying. Would be nice to be able to program my i3 for details of charging rate curve and endpoint but my understanding is the i3 software is not that flexible on its own.