Software update needed for HV battery capacity check

[alohart]

It's better to have the car plugged in and be conditioned than not. My garage hits 100 F inside in the summer. If I don't have my car plugged in, it's worse for the battery to sit in that heat all day.

I'm pretty certain that battery pack cooling becomes inactive after the charge level reaches 100%. If this weren't true, there would be no need for the battery pack preconditioning function because it would happen automatically. So leaving an EVSE plugged in won't guarantee that your battery pack would remain cool if the ambient temperature is hot. One trick that some have used is to set AC Level 1 charging to the minimum speed in iDrive and plug in an AC Level 1 EVSE like the occasional use cable included with an i3. If the charge level isn't near 100%, charging would occur slowly during which time battery pack cooling would be active.

I don't live where battery pack cooling is necessary when parked and not charging, so I have no experience with this. If cooling can occur when parked with an EVSE plugged in even when the charge level is 100%, please correct me.

 

[Arm]

I'm pretty certain that battery pack cooling becomes inactive after the charge level reaches 100%. If this weren't true, there would be no need for the battery pack preconditioning function because it would happen automatically. So leaving an EVSE plugged in won't guarantee that your battery pack would remain cool if the ambient temperature is hot. One trick that some have used is to set AC Level 1 charging to the minimum speed in iDrive and plug in an AC Level 1 EVSE like the occasional use cable included with an i3. If the charge level isn't near 100%, charging would occur slowly during which time battery pack cooling would be active.

I don't live where battery pack cooling is necessary when parked and not charging, so I have no experience with this. If cooling can occur when parked with an EVSE plugged in even when the charge level is 100%, please correct me.

It's not inactive if the car continues to be plugged in...at least for high temperature situations. I know this for a fact because on many occasions during the summer, I have opened the garage door hours after the car has finished charging only to find the thermal management system active and the EVSE on....meaning the car is pulling current to maintain battery capacity of 100%. I imagine that if I had a "limiter" on my i3 where I could set an upper limit of charge like one can on a Tesla, it'd do the same to maintain that charge while cooling the battery.

I've never see this happen in cold temperatures perhaps because A) it never gets cold enough where I live and B) heat probably damages a battery physically more so than cold weather (even though battery performance may be less in cold weather).

Even BMW recommends keeping the car plugged in and fully charged whenever possible.

I see no issue with this at least for me. I now drive the 33kW BEV version which...for me has plenty of range. Even with a degradation of 30%, it's more than adequate. I can understand someone with a smaller battery pack worrying about degradation however.

I believe my car has been flashed with the upgraded software. So any level of degradation from this point on (for the next 5 years or 35000 miles) needs to happen between now and then. But I've posted earlier, my battery levels seem pretty solid for now. If they degrade quicker than anticipated, I'll deal with it at that time.

 

[djbrh]

I don't know if I agree with that. What proof is there that rapid battery degradation will occur because they allow more useable battery?

Because that’s how this particular battery technology works. It’s why Tesla recommends NOT charging past 80% unless you NEED to. It’s why you’re not supposed to charge a Tesla from 80->100% in that case until *right* before you leave if you’re gonna do it. You can ignore both of these recommendations if you want, but they tell you up front if you do that it will shorten your battery’s life.

That’s why BMW only allows 80% to be used in the first place. I’m not sure how you can argue this, tbh.

And I’m not saying a Tesla battery, charged daily to 100%, is going to “degrade rapidly.” I’m saying it’s going to degrade a lot more rapidly than one that ISN’T charged that way, but what “rapidly” is in this case isn’t well defined. What is quite likely, however, is that a 7yo or so battery that’s already degrading and then has more of that ceiling opened up *is* likely to decline pretty rapidly.


—Donnie

These are assumptions based on fast charging. If you're home charging most of the time, it's not an issue.

It's better to have the car plugged in and be conditioned than not. My garage hits 100 F inside in the summer. If I don't have my car plugged in, it's worse for the battery to sit in that heat all day.

You are badly missing a key distinction: the i3, when charged to “100%” on your dash, is only charged to 80% of the capacity of the pack as built. It won’t ever use that upper 20%, no way, no how. That’s by *design*.

So yes, you are correct, that charging an i3 to 100% is *fine*. It’s charging a Tesla to 100% that’s *not* fine, because with a Tesla, 100% on the dash is 100% of the battery as it’s built.

Now, the problem is this software update that’s being given to people with batteries that have degraded below BMW’s promised acceptable level. We’re all measuring what our car’s battery is capable of by how many miles it goes. If your car used to go 65 miles on a charge and now it’s degraded to the point it only goes 50, well, BMW *should* replace your battery pack. But they realized that instead of that, they could open up that upper 20% that they previous had locked out (or at least some of it), so that’s what they’re doing.

So you, as a consumer, are used to charging every day to 100% and that’s fine because BMW really only let it charge to 80% and you had no idea and the battery life should be really good doing that. Except 7 years later, with one year left on that warranty, it’s not. So what should BMW do? Replace your pack. What are they doing instead? Opening up some of that upper 20%. So now when you charge to 100% every day like you’re used to doing, instead of it topping out at the magic 80% of built capacity, which is safe for the life of the battery, it’s topping out at 90%, which *will* degrade the battery EVEN faster. But they don’t care, because they only need to buy ONE MORE YEAR.

This is what’s happening. I don’t know how to explain it to you any more clearly.


—Donnie

 

[Arm]

Do you have any proof that BMW is doing this? If so, where's the data to prove it? I'm not saying it's not happening but I would want to see the proof.

Again. If my car has sufficient range to compensate for battery degradation, it's less of an issue. It's like any other issue I'd have with a car. An 8-10 year old ICE vehicle certainly doesn't perform as well as it did the first day I got it. At that point, it's an 8 year old car. My expectations change. People are much harder on EVs than regular cars for some reason.

Most people don't even keep cars that long. If you are one of the few who do, then this issue is unfortunate for you. But for most people, it's a non-issue and manufacturers design their cars for the majority not the small outliers. That's how it is and has always been.

It's funny....if Tesla improved their battery capacity via software, people who would be praising it. When BMW does it, they are slammed for it. I wonder how Tesla improves their 0-60 times with over the air updates? I'm sure that negatively affects battery health as well since they are now asking more power out of the battery to offer better performance.

I understand your concern but you're putting way too much effort into thinking about this in my opinion. Frankly, I think the issue for people who fall into this category is the fact that their cars had crap range to begin with (65-80 miles is not even a starter these days) and any variation of that is a huge issue. Perhaps it's time to upgrade to a vehicle with greater range tolerance?

BTW, Tesla's batteries also do have buffers. That is not true that when you charge a Tesla, it's all the way to 100%. And Tesla's vampire drain is large.

https://electrek.co/2016/12/14/tesla-battery-capacity/

 

[alohart]

You are badly missing a key distinction: the i3, when charged to “100%” on your dash, is only charged to 80% of the capacity of the pack as built. It won’t ever use that upper 20%, no way, no how. That’s by *design*.

That's simply not true! 87% of a 60 Ah battery pack's nominal new 21.6 kWh gross capacity is usable, 18.8 kWh. The 13% of unusable capacity is split between low and high charge level buffers. When new, ~8% of the gross capacity is unusable at the low charge level end while ~5% is unusable at the high charge level end. This is explained in detail in David Bricknell's excellent book, Electric Vehicles and the BMW i3 (60 Ah and 94 Ah).

So when a new 60 Ah i3 was charged to an indicated 100%, the battery pack's charge level was actually ~95%, not 80% as you claim. There was very little high charge level unusable buffer on a new 60 Ah battery pack.

Over time, the BMS might be increasing the size of the high charge level buffer. That seems to be what the mi3 and electrified apps as well as BMW's ISTA+ indicate. mi3 indicates that the battery pack in our 2014 BEV has degraded by 23% (77% state of health) with the high charge level buffer being 24.7% and the low charge level buffer, 8%. This is consistent with the loss of our i3's actual range, and the current Batt. Kapa. max value of ~15 kWh. However, the average cell voltage when fully charged, 4.089 V, at an average cell temperature of 29.18 ºC seems very high for an actual charge level of 75.3%, so I'm suspicious that the high charge level buffer's size has been increased. Based on the maximum average cell voltage, it seems more likely that the capacity of each cell has decreased by 23% with the buffer sizes remaining unchanged.

 

[djbrh]

If I’m understanding Art’s post correctly, my 80% number is wrong, but it still sounds like the overall theory is correct. And I had no idea there was head and tail buffers, but I don’t think that changes the actual problem, either. So it’s some larger percentage and it’s sort of in the middle instead of just on one end.

Basically, BMW designed it this way to help prevent degradation, then warrantied it to a level of degradation. Then when some degraded far enough that it should have triggered the warranty, instead BMW’s software “upgrade” really just erases *some* amount of those buffers. And since the purpose of those buffers is to preserve battery life, it’s likely you’re going to make it just past warranty and then the thing is going to degrade further.

I don’t think it’s unreasonable to want what my warranty promised me. I’m not sure how wanting that is wrong.

I hope the theory that they’re just unlocking that buffer space is wrong and they’ve somehow magically found more battery capacity through software in some way that doesn’t degrade the battery faster. I have my doubts, though.


—Donnie

 

[eNate]

...I had no idea there was head and tail buffers, but I don’t think that changes the actual problem, either.

Yes and no.

BMW is around 5% at the top and slightly more at the bottom, but this is in line what other manufacturers do.

Technology evolves, and for example, VW uses a newer BMS that reserves only 2% at either end, as their contractor (NXP) claims they can monitor individual cell conditions down to one one hundredth of a volt.

Tesla, meanwhile, sells "base model" cars with extra "hidden" capacity that can be unlocked with a simple phone call and a credit card.

That leaves BMW with a legally grey "out," VW with nowhere to go but a replacement battery, and Tesla with a perfectly legit way to address a battery claim.

Because BMW never states what percentage of buffer is necessary versus what percent is simply "reserved for future use," I wonder how a denied warranty claim would stand up legally. There's a possibility that some of that extra capacity is there precisely for that purpose — for future use — since we're given no way to set a charge limit in our i3s. Sort of like Tesla's hidden capacity.

I think it would be up to us owners to prove that reducing the buffer has a deleterious effect on battery health after the change is made.

 

[djbrh]

...I had no idea there was head and tail buffers, but I don’t think that changes the actual problem, either.

Yes and no.

BMW is around 5% at the top and slightly more at the bottom, but this is in line what other manufacturers do.

Technology evolves, and for example, VW uses a newer BMS that reserves only 2% at either end, as their contractor (NXP) claims they can monitor individual cell conditions down to one one hundredth of a volt.

Tesla, meanwhile, sells "base model" cars with extra "hidden" capacity that can be unlocked with a simple phone call and a credit card.

That leaves BMW with a legally grey "out," VW with nowhere to go but a replacement battery, and Tesla with a perfectly legit way to address a battery claim.

Because BMW never states what percentage of buffer is necessary versus what percent is simply "reserved for future use," I wonder how a denied warranty claim would stand up legally. There's a possibility that some of that extra capacity is there precisely for that purpose — for future use — since we're given no way to set a charge limit in our i3s. Sort of like Tesla's hidden capacity.

I think it would be up to us owners to prove that reducing the buffer has a deleterious effect on battery health after the change is made.

If the buffers are indeed that small then it would seem to me that they must be unlocking nearly all or all of it to get some of these capacities back within warranty specs, though, no? And if they’re using it all, well, it would further seem fairly easy to “prove” assuming it does actually degrade pretty fast after the warranty. I mean if it doesn’t then obviously there’s no reason to care…BMW was right and I (and others, I’m not the only person worried about this) was wrong. But it seems likely an already degrading battery will go downhill faster once those buffers are unlocked. *shrug*


—Donnie

 

[3pete]

it seems likely an already degrading battery will go downhill faster once those buffers are unlocked.

This seems likely, but that doesn't necessarily mean it's true. A couple points:
1) It's not necessarily the software giving access to the 'buffer' that the car had when it shipped, it's possible that the software is giving back access to battery capacity that the BMS essentially walled off through use of the car. Either one of these could be valid under certain scenarios, or they could be a short-term band-aid just to get them past the warranty threshold.


2) BMW has a lot more real-world data on early i3s now than they did in 2014 and they could have realized some of their assumptions on battery degradation were unnecessarily conservative and they're comfortable with giving back some of the capacity that the BMS has declared unusable. BMW could be motivated by warranty claims looming but I think it's worth noting that other manufacturers have added range to their EVs with software updates even though they have many years left on their warranty. Most recently, Audi is adding about 3.5kWh to the 'usable' section of the 2019 e-Tron's battery through a software update even though it's nowhere close to being 8 years old.
https://www.audi-mediacenter.com/en...oftware-update-for-20192020-model-years-14346

I don't think they'd do that if they thought it would contribute to faster battery degradation and risk increased warranty claims.

I completely agree that BMW doesn't seem to be handling this in the best way possible though. A little more transparency would go a long way!
Considering they've discontinued the i3 and looking at their new EV offerings, it seems like they don't really care too much about i3 owners though.