Monday, September 25, 2017

BMW i3 Poised For 2nd Battery Upgrade. Hopefully A Naming Upgrade As Well…

The 2018 i3 Sport made its debut at the Frankfurt Auto Show. Both the i3 & i3 Sport models will start the 2018 production year with the same 33.6 kWh battery as the current i3 has. It's believed later in the year BMW will upgrade the battery to a the new 44.2 kWh pack, adding another ~40 miles of range.

Fresh off of the Frankfurt introduction of the new BMW i3 exterior refresh and new i3 Sport for 2018, BMWBLOG is now reporting that they have confirmation that 2018 will also bring a new, larger battery option to the i3, albeit later in the year.

In mid-2016, BMW introduced the current 33.6 kWh battery which was an upgrade from the 21.6 kWh battery previously available. That bumped the i3 BEV’s 81 mile range to 114 miles per charge. The new battery, which is being introduced sometime later in 2018, is rumored to have a total capacity of 43.2 kWh and offer an EPA range rating of 150 – 155 miles per charge.

Customers that opt for the range extended version of the 43.2 kWh i3 will have about 230 miles of total driving range without the need to stop to recharge or refuel. The increase in all electric range will place the i3 in a virtual tie with the new Nissan LEAF for the second longest EV range behind the Chevy Bolt, in the “everybody but Tesla” class of electric vehicles. That is of course, until Nissan launches the 60 kWh LEAF, which isn’t expected to be available until the 2019 model year LEAF is out. Audi and Jaguar are also expected to introduce their respective long-range EVs sometime in 2018, and they will also leapfrog the i3 and LEAF in range.
An i3 battery pack being assembled at BMW's Leipzig plant.

One thing I’d like to see BMW do when they introduce the new battery is stop referring to the battery by the amount of Amp hours each cell holds. It’s a completely useless metric, and one that only causes further confusion among potential buyers. No other carmaker uses the Amp hour (Ah) metric to identify their battery packs. It would almost be as if they started to distinguish their internal combustion engines by their bore & stroke instead of the traditionally-used displacement in liters. It just makes no sense.

Every electric car manufacturer today refers to the battery by the amount of energy it can hold in kilowatt hour (kWh), but for some reason, when BMW introduced the new, larger battery for the 2017 i3, they decided to use the Ah metric and called it the 94 Ah battery instead of the 33.6 kWh pack.
BMW has been advertising the current i3 as the "94 Ah Sedan". The problem is, "Ah" doesn't mean anything to most customers, and is fact just confusing to them. BMW should drop using Ah to describe which battery pack the car has. Just give us the size of the pack in kWh, and the EPA rated range. There's no need to complicate this.

Critics claimed it was intentionally done, to confuse buyers and make the battery sound larger (94 is a bigger number than 33.6), and seem like it was comparable to Tesla’s battery offerings (75, 85, 90 & 100 kWh). Personally, I don’t agree with that assumption, I think it was just a case of BMW product planners wanting to distinguish the new battery as being better, and it was the first time they ever offered a new battery option, so they used the name that their supplier Samsung, uses.
In any event, I’m happy to hear that BMW will be rolling out the second battery upgrade in two years. The i3 will then have used three different batteries in the first five years of availability, proving that BMW is continuously willing to improve the i3 as better battery technology becomes available.

My advice to BMW product planners: Drop the Ah designation, please. It’s only confusing your customers, your client advisors and in some cases even journalists writing about the i3. Simply do what every other EV maker does and call it by the total size of the battery pack, in kilowatt hour. In this case, the new i3 will be the 43 kWh i3. It’s easy, most buyers understand it, and client advisors won’t have to spend an hour explaining energy density, voltage, cells, and modules to every potential customer that asks how the battery compares to the batteries of the other EVs on the market. 

Friday, May 5, 2017

BMW i3 Long Term Battery Capacity Report: Better Than Expected

The heart of any electric vehicle is its battery. This BMW i3 cutaway shows the battery removed from drive module. 
When it comes to electric cars, it’s all about the battery. Well, it’s not quite that simple, but given how important the battery is to the cost, range and performance of the vehicle, it’s pretty close.

When someone is considering purchasing their first electric car, they will certainly have a lot of questions.  The one question that seems to be on nearly everyone’s list is: “How long will the battery last?”

The problem is, it’s been very hard to answer that question authoritatively because we just haven’t had enough data.  That’s because modern electric cars that are powered by high-voltage lithium ion battery packs have been on sale for less than ten years, and long term testing results simply weren’t available.  In fact, the Nissan LEAF was the first high-volume all-electric car brought to market, and that model has only been on sale for a little over six years.

Nissan’s early LEAF battery woes:

Some of the early Nissan LEAFs had premature battery degradation issues, particularly those that were in service in hot climate areas like Arizona. It became such a problem that Nissan changed the chemistry of their batteries in 2015 to a more temperature-tolerant version and announced an improved battery warranty to ease the concerns of current owners and future buyers. The negative press from this problem threatened to set back the advancement of all makes of electric cars, because it brought to light the possibility of EV battery packs failing earlier than previously predicted.  However, this was a self-inflicted wound, in my opinion. Nissan elected to bring the LEAF to market with a simple air-cooled battery pack, instead of employing a sophisticated liquid-based system like Tesla and GM were already using back then. The decision to do so allowed for a lower MSRP, as well as a shorter R&D period, but most likely contributed to the early degradation problems that some LEAF owners experienced.
An early Nissan LEAF battery pack
Tesla & GM batteries performing well:

Fortunately, the other mass-market EV manufacturers that launched their respective cars earlier in the decade have not had the same battery degradation issues that Nissan experienced. Both the Chevrolet Volt and the Tesla Model S have complex, liquid-based thermal management systems and the battery packs of both of these vehicles seem to be holding up very well over time.

In fact, Plug In America has been collecting data from hundreds of high-mileage Model S owners, and has built a database of battery degradation rates. They’ve found that the average Model S owner is experiencing a loss of only 2.3 miles of range for every 10,000 miles driven.  Considering all Tesla vehicles offer more than 200 miles of range, an estimated loss of only 23 miles of range for every 100,000 miles of driving is very good. Obviously that the rate of 2.3 miles of loss per 10,000 will likely accelerate at some point, because battery capacity loss isn’t linear, but all of the vehicles in the study had more than 50,000 miles. That made them good candidates to study the loss of range over time.  General Motors has similarly reported no problems with Volt battery packs experiencing early capacity loss.
The happy new owner on delivery day, May 21st, 2014.
How’s my BMW i3’s battery holding up?

BMW launched their first retail all-electric car, the i3 in Europe in late 2013. Here in the North America, the first i3 deliveries started in May of 2014. I actually took delivery of the first i3 REx in the US and I drive more than the average person, so I have one of the highest mileage i3s on the road. I’m a couple weeks shy of my three-year anniversary with the car and I have 70,000 miles on the odometer. I know I’m only one sample, but if what I’ve experienced turns out to be the norm, then i3 owners are going to be very happy with how their battery holds up over time. BMW is one of the few EV manufacturers that offer a clear battery capacity loss warranty, and has guaranteed at least 70% capacity for 8 years or 100,000 miles. The stated usable capacity for the 2014 i3 is 18.8 kWh. Therefore, the battery would need to degrade to 13.15 kWh to trigger a warranty claim.

Methods used to arrive at my conclusion

I’ve found that even though the range estimator does a pretty good job for daily driving, it’s not nearly accurate enough to use for recording and documenting the true range of the vehicle. Instead, I have two other types of data points that helped form the basis of my conclusions regarding the current state of health of my battery.

First, I frequently record my trip mileage and remaining state of charge before I plug in. This gives me a more accurate view of how far I can go per charge than what the range estimator provides. (Frequently called the GOM or Guess-O-Meter by some EV enthusiasts) The fact that I have an i3 with range extender complicates it a little, because the range extender turns on when the SOC in under 7%. Therefore, I only have access to 93% of the usable capacity of the battery before the REx fires up.  The simple formula I use is arrived at by dividing the number of miles driven by the percentage of battery used. That value will be how many miles (or what percentage of 1 mile) the car has traveled for every 1% of battery used.  I then need to multiply that by .93 (100% minus the 7% buffer) and I then have how many miles the car would have been able to go if I had continued driving until the REx turned on.


Starting SOC: 100%
Ending SOC: 45%
SOC used: 55%
Miles driven: 45
(45/55) x .93 = .76 (76 miles per charge)

Starting SOC: 92%
Ending SOC: 8%
SOC used: 84%
Miles driven: 67
(67/84) x .93 = .74 (74 miles per charge)
The car is still estimating 22 miles of electric range after driving 53 miles. I can pretty much still bank on 72 to 78 miles of range with normal driving in Comfort mode in temperatures above 60 degrees. 
When using this method to gauge battery performance it’s important to record the ambient temperature if you live in an area that experiences moderate to extreme cold and hot temperatures. These temperature swings will affect the car’s range. The cold weather has a much more dramatic effect than hot weather does, and it’s important to compare the present figures with past data from the same time of the year, when temperatures were similar.  For the purpose of this comparison I’m stating figures that were gathered when the temperatures were between 60 degrees and 80 degrees, which is close to the optimum operating temperature range for the i3’s battery. For instance in the coldest months of the year, with temperatures below 20 degrees, my average electric range was as low as only 55 miles per charge.

The second method I used involves the car’s onboard diagnostics tool meant for service personnel, called the hidden service menu. This offers an estimate of the battery’s state of health. The onboard computer calls it the “Batt.Kapa.Max” and it displays the amount of usable capacity (not total capacity) in kWh. This number isn’t exactly accurate – it’s an estimate, and I caution i3 owners from looking at it and treating it as a precise fact. In order to use this estimate to really help you understand and monitor your battery’s capacity, you need to check it frequently, and chart the readings on a graph. The number provided can swing as much as 2 kWh up or down on a daily basis, so it’s clearly not precise.
The Batt.Kapa.max reading in the hidden service menu is averaging about 18.2 kWh after three years and 70,000 miles. That's down from about 19.1 kWh when the car was new
Don’t panic if you check it one day and the reading is unusually low. What I’ve found is that to get a good reading you should drain the battery as low as you can, and then check the reading once it’s fully recharged. The battery should also be as close to 70 degrees Fahrenheit, as colder temperature give a false reading that is slightly lower than the true value.  BMW has warned against relying on this since it is an estimate. The only way to get a truly accurate measurement (for warranty claims) is to have a BMW service department perform a test.

BMW claimed that the usable capacity for the 2014 - 2016 i3s was 18.8 kWh. However, some owners have seen as high as 19.9 kWh available when they’ve checked the Batt.Kapa.Max reading. This can either be attributed to an inaccurately high reading (remember this is not a precise reading), or that BMW has actually opened up more than the 18.8 kWh they claim is available. The highest reading I have ever seen on my car was 19.2 kWh, and the lowest was 16.1 (in the winter). When my car was new the average reading in favorable conditions was about 19 kWh. Today, my average reading is now about 18.2 kWh. If these average readings are correct, it would mean that I’ve lost about .8 kWh of usable capacity after 36 months, 70,000 miles and approximately 1,000 complete charging cycles.  (I’ve probably plugged in closer to 2,000 times, but my average trip between plugging in is only about 37 miles).

The .8 kWh loss of usable capacity seems to be in line with my recorded range data.  Since I’m averaging about 4 mi per kWh, I should be witnessing a loss of about 3 miles of range, (.8 x 4 = 3.2) which is exactly what my range readings have recorded. When the car was new, I was averaging 78 miles per charge in favorable weather conditions; it’s now down to 75 miles per charge. That’s pretty impressive since the EPA range rating for the 2014 i3 REx was 72 miles per charge. So I’m still averaging more than the EPA range after three years and 70,000 miles.  Since both measurement methods equate to about a 4% capacity loss, I’m pretty confident that they validate each other. Therefore, the 4% is correct, or at least very close to the actual capacity loss

With careful driving, I can still get more than 80 miles per charge. On this recent trip I was able to get 84 miles without the range extender turning on. In order to get 80 miles I need to keep my consumption to 5 miles per kilowatt hour or better. 

This should be very encouraging for existing i3 owners, and help to alleviate any anxiety that those currently considering the purchase of an i3 might have. I have to believe that the sophisticated thermal management system that BMW used in the i3 is partially responsible for the excellent long-term performance of the Samsung battery cells used in the car. If my experience holds true for the majority of the i3 fleet, this is good news not only for BMW, but also for the entire EV industry. Battery capacity loss concerns are on the minds of many potential consumers that are interested in entering into the world of electric cars. Continued positive reports on battery life will help to alleviate those worries and give the entire industry a boost of confidence.

However, as I said above my experience is just one data point, there’s a lot more information needed before we know conclusively how long these packs will last, but this indeed very encouraging. Based on my personal findings, I suspect that BMW won’t have to worry about paying out too many battery capacity-loss warranty claims.

Friday, April 14, 2017

NY International Auto Show: One on One Interview With BMW's EV Boss

BMW i North American Product & Operations Manager, Jose Guerrero
I had the opportunity to sit down with BMW NA’s top man when it comes to electric vehicles, Jose Guerrero at this year’s New York International Auto Show. Guerrero is BMW i’s North American Product & Operations Manager, and has been working in BMW’s electric vehicle programs since the ActiveE pilot program began in 2011.

Just before we started the interview, it was announced that the BMW i3 was named the inaugural winner of the World Urban Car Award, so I asked Guerrero for his thoughts on the i3 winning yet another award.

“I think it’s a testament to the car. Even though we’re making incremental improvements, like software updates and offering a moonroof, the only real dramatic improvement we’ve made is the addition of the 94 Ah battery. That said, the car is still remaining relevant with the backdrop of increased competition in this segment.  So, to see the continued accolades for a car that launched over three years ago is a good sign, and rewarding to us. But we’re not stopping; we’re continuing with product improvements on a fairly short basis, verses the traditional BMWs.”

There isn’t much more news to report on the i3 & i8 at NYIAS this year. The i3 is scheduled for a minor refresh in 2018, but BMW isn’t publically commenting on that yet. It’s been widely speculated that in addition to the refresh, a new i3 Sport model will be offered, and many spy photographs of what appears to be this version have already been posted online. I wouldn’t expect BMW to comment on this until the formal introduction of the 2018 i3, which will likely happen at the Frankfurt Motor Show in September.
BMW i & BMW iPerformance vehicles are side by side at NYIAS
We then moved to the topic of BMW iPerformance vehicles, which have a prominent placement on this year’s show floor at NYIAS. BMW now offers four plug-in hybrid iPerformance vehicles, the X5-40e, 740e, 330e and the just-introduced 530e.  Guerrero said they are selling very well, and the dealers are selling them as quickly as they come in. He added that the supply is going to increase as the year goes on, but has faith that the dealers will continue to sell them nearly as quickly as they get them because the demand is there.

I then mentioned that some EV enthusiasts are critical of PHEVs that have low all-electric ranges, like the iPerformance line offers, and asked for his thoughts on that.

“The market for iPerformance is still in the early stages, and the success we’re having is really taking place at the dealership level. With BMW i, we had to work harder to find the customers and cultivate sales for the i3. With iPerformance vehicles, people are coming in off the street not even knowing about our plug-in offerings. Yet they are being converted because of the driving experience and the overall cost of ownership. There’s a job for BMW i electric vehicles, and there’s a job for BMW iPerformance plug-in hybrid vehicles. Not everybody is ready today for a fully electric vehicle, even if his or her driving profile matches what the i3 offers. We understand that this switch to EVs won’t happen overnight. We need to get people used to plugging in their cars and experiencing the benefits of electric drive first. That’s the job of iPerformance vehicles, it’s really converting a lot of people to the plug. That experience may lead them to purchase a longer range PHEV the next time around, or it may lead them to an all-electric car. Not everybody is ready for an all-electric vehicle at this point. I am (Guerrero has been driving an i3 since 2014), I know you are (referring to me), but for many who aren’t, iPerformance vehicles are the sweet spot.“
Guerrero speaking at an unidentified BMW event 
I then asked him if BMW of North America is ever going to participate in the i3 Battery Retrofit Program that BMW AG announced last year. The program is currently only available in a select few European countries, and BMW of North America hasn’t commented on whether they will ever offer a battery upgrade program. I think I was able to get (kind of) the first official confirmation that BMW of North America will offer a version of a battery upgrade/retrofit program at some point in the future, and that they are already testing internal fleets of retrofitted i3s.

“Absolutely. Even though we made the decision to not offer this option today, we’re still conducting our own internal study with a fleet of i3s that we’re retrofitting with battery upgrades to learn from and study for the US-specific group. Even though we don’t have a consumer offering, internally we have fleets running around learning the benefits and challenges. So we’re not stopping, just because we didn’t initially offer it. As long as there is a viable consumer program that people would buy, of course we will offer it. There’s also a sustainability side to this. There’s stationary energy storage, there’s the smart home and solar story that are tied to the ecosystem with home energy storage. We know even if there isn’t a car-to-car alone business case for upgrade, it works from the whole 360-degree sustainability model.  We are looking at this holistically; we want to say to the customer: Here it is; solar, battery for energy storage, the Internet of Things, and your electric car. This is how it all works.”

At this point my allotted interview time was coming to an end so I asked Guerrero if there was anything he’d like to add to our discussion.

"First and foremost, I’d like to say we’re listening to our customers. We’re taking in all of the feedback we’re getting from our current plug-in customers and our dealers, and we’re learning from that. Things like the numeric state of charge gauge. Our customers asked for it and we added it. Lesson learned. The next generation of electric vehicles we offer will benefit from all of the feedback we’re getting today. We’re going to continue to improve and innovate. But we realize the future is always changing, whether it be inductive charging, or high speed DC fast charging we will be there and continue to innovate. However, we will still rely on customer feedback, so we always want to keep that conversation alive.”

Tuesday, April 11, 2017

Product Review: ClipperCreek HCS-40p EVSE

My i3 charging from the HSC-40p. You can see my older ClipperCreek CS-40 all the way on the left.
When it comes to electric vehicle charging equipment, there’s certainly no shortage of choices. Even though it’s a relatively new market, there are dozens of manufacturers selling products that allow owners to safely and conveniently charge their electric cars. Although this equipment is commonly referred to as a "charger" or "wallbox", the proper term is actually EVSE, which stands for Electric Vehicle Supply Equipment. 

These devices don't actually charge the car; they provide the electricity to do so. That's because the actual charging equipment is built into the car. The EVSE's purpose is to safely deliver the correct amount of electricity to the onboard charging equipment. 

Now that electric cars are beginning to gain momentum in the marketplace, there are a lot of companies jockeying to get a market share of the EVSE business. The vast majority of these companies have been manufacturing and selling EVSEs for less than six years. However, there is one EVSE manufacturer that has more experience than any other company, with roots that go back into the early 1990s, as well as supplying the home charging equipment for the Tesla Roadster. ClipperCreek, has been making EV charging equipment for over twenty years now, and manufactures all of their products in the USA.

I’ve been using ClipperCreek products to charge my electric cars since 2009, as BMW choose ClipperCreek as their partner to provide the charging equipment for the MINI-E Trial Lease Program.  I’ve never had any problems with any of my ClipperCreek equipment and I still use my original CS-40 EVSE that came with my MINI-E.

However, I also have a version of the latest generation of EVSEs from ClipperCreek, an HCS-40p.  The HCS-40 & the HCS 40p can supply 32 amps at 240v, and deliver up to 7.7kW to the vehicle.  The only EVs currently on sale that can accept more than 7.7kW at 240v are the Tesla Models S & X, and the Mercedes B250e (which uses a Tesla-made onboard charger). So the HCS-40 line of EVSEs is more than powerful enough for the vast majority of today’s electric vehicles. 

For instance, my 2014 BMW i3 can only accept up to 7.2kW, and the rest of BMW’s line of PHEVs, including the i8, the X5-40e, the 330e, the 530e and the 740e, are all limited to a maximum of charging at 3.7kW. This is because plug in hybrid electric vehicles (PHEVs) have smaller batteries than full electric cars do, and thus charge quicker and don’t require such high speed charging.
ClipperCreek uses high quality connectors with a rubberized grip for added comfort when plugging in.
However, if you do want more power, for instance to future-proof your garage, ClipperCreek has you covered. They also sell the HCS-50 & HCS-50p, which both deliver 40amps of power, which translates to a maximum of 9.6kW. The HCS-60 steps up the delivery to 48 amps and a full 11.5kW. For the ultimate in home EV charging, the CS-100 can deliver 80 amps to the vehicle, which is a whopping 19.2kW.  This power delivery rivals the speed that some of the lower-powered DC Fast chargers, but currently only Tesla vehicles can accept such high a level of power from a level 2, 240v EVSE. I believe that's going to change in the coming years, and many EVs will come standard with higher power level 2 charging capabilities of at least 9.6kW.

I received my HCS-40p about a year ago and it’s lived up to the reputation that past ClipperCreek products have earned.  Made from airline-grade plastics they are probably the toughest EVSEs on the market. There’s even a video of ClipperCreek employees beating an HCS-40 with a baseball bat, and the bat broke before the station did:

The HCS line comes in both hard-wired and plug-in models. The plug-in offerings are distinguishable by the “p” at the end of the model name. If it has the “p”, than it’s the plug in version. You can order the plug-in versions with either a NEMA 14-50 or NEMA 6-50 plug.  Therefore, you can have your electrician install the 240v you choose before you even buy the EVSE. 
Two screws & it's done!

Personally I prefer having the plug in option, which is why I got the HCS-40p. It’s a little more expensive, ($589 compared to $565 for the HSC-40) but it offers the flexibility of easy installation – you simply screw it into the wall and plug it in. Having the plug also means it’s not permanently installed in one place.  If the need arises, you can unplug it, remove the two screws and relocate it. This can also work very well if you need to take the unit to a second location, like a summer house. All you need to do is install the outlet in the second location and just take the unit there when you need to.

I test electric vehicle charging equipment and review new products, so you can see how the HCS-40 compares in size to many other EVSE options available today in the picture below. It is one of the larger packages available today, and the body of the unit is used for cable management, you simply wrap the cable around it. There is a separate connector holster included that you can locate where it’s most convenient, as well as a lock and key so you can deter someone from unplugging your car.
My "Power Wall"

ClipperCreek has an extensive list of electric vehicle charging equipment and probably offer more options than any other company. All of their Level 2, 240v EVSEs come standard with a 25 foot cable, which is optional on the products of many of their competitors. Many EVSE purchasers don't consider the cable length when they buy one. I think some may assume they all are a standard length, but that's not true. Some EVSEs come standard with a 15 or 18 foot cable, and that may come up short in certain circumstances. With a standard 25 foot cable, you are pretty much assured you can reach any point in your garage, and even outside the garage if you park close enough. 

Note: I received the HCS-40p from ClipperCreek for free for the purpose of testing, feedback and product review. No other compensation was made.

Friday, March 24, 2017

Incorrect State Of Charge Readings Causing Problems For i3 Owners

With the i3 REx, Reduced Power can occur if the operator continues to use more energy than the REx engine can produce. Examples of this would be continued high speed (over 70 mph) driving or long, sustained hill climbing. However this new problem that has plagued some i3 owners isn't caused by over-taxing the REx. 
Someone once said, "You could always tell the pioneers by the arrows in their back."  A recent software bug has cropped up that seems to be affecting many of the early build and higher mileage i3s that are mostly driven by the early adopters. The problem causes the car to go into reduced power mode, or in some cases shut down without warning when the display shows about 5% - 6% battery remaining.

In mid 2016, BMW released a software update, (version 16-07-501) that was supposed to correct the issue, but for some unknown reason it didn't work on all of the vehicles. They then sent out letters to the early buyers to inform that they need a software update. Recently though, the problem seems to have become more and more common, with many owners reporting it. I'm not 100% sure if that initial software update did what it was intended to, or if it actually exacerbated the issue, because it really seemed that the problem became more widespread once people had the new software installed. 

Perhaps it was just timing that made it seem that way because the cars are getting older and natural battery capacity loss is occurring. Also, the colder weather came and that could have played a role in magnifying the issue. BMW did realize the new software didn't do what it was supposed to, and quickly issued a new version, as well as a service bulletin (B61 20 16) which informed the service centers of the problem and how to correct it. However, some centers haven't been quick to pick up the problem, and I've had more than a few i3 owners ask me for help getting this problem resolved. 

There are probably dozens of service bulletins issued by BMW every month, so it's understandable that some centers might be a little slow to catch every one, but it's now more than six months into the problem and there are still many centers that aren't able to diagnose the problem when a car comes in with it, and that's just too long. One potential reason they were having trouble diagnosing the problem is that the symptoms of this issue are very similar to how the car may act under normal operation when the range extender is over-taxed. It's been well documented that the range extender has limits. If you drive at highway speeds up continuous steep inclines then there will come a point that the range extender cannot supply enough energy to maintain the speed. The car will then go into reduced power mode and slow down to about 40 mph. However, speed or excessive hill climbing isn't the root cause of this issue, it's actually an incorrect adaption value of the battery's state of health, even though the results are similar. 

A simple explanation of the problem is that the affected cars are incorrectly reading the battery's state of charge (SOC), and slightly overestimating it. This doesn't present any real problem unless you discharge the battery to well under 10%. At such a low state of charge, it's very important to have as accurate of a reading as possible, since every percent counts when you're trying to make a destination. Calculating the precise state of charge of a battery is very difficult, and with all EVs, the displayed SOC is a close approximation of the actual SOC, it's not a perfectly accurate value. 

The 2014 to 2016 i3s have about 19 kWh of usable battery capacity, when new. Like all batteries, as they age they lose capacity. If an i3 battery loses 10% of its original capacity, then the usable capacity is roughly 17 kWh. If the car doesn't properly recognize the loss of capacity, it can miscalculate the remaining state of charge. That is what's happening with some of the older i3s. The onboard battery management system (BMW calls it the SME High Voltage Battery Module) isn't adjusting quickly enough to the capacity loss, and it is overestimating the actual remaining level of charge. 

What this means is, if you drive an older i3, you may think you have slightly more range left than you actually do. There have been reports of a few i3 BEV drivers having the car slow down to reduced power mode, then crawling to a halt when the SOC gauge states that there is another 5% or 6% battery available, and 4 or 5 more miles of range still "in the tank." Most i3 BEV owners don't drain the battery to such a low state of charge, so they'd never even know their car is affected by this issue. 
A quick look at the display tells you all you need to know about this issue. My car states that it is at 5% state of charge, but  most of the 11 power blocks on the right side of the ePower gauge are grayed out. That means the car is in reduced power. At 5% SOC, I shouldn't be in reduced power unless there was a severe temperature issue (way too high or too low) with the battery or motor, which wasn't the case.  These power blocks shouldn't start disappearing until the state of charge is below ~2%. Since the power blocks are nearly all gone in this picture, my true SOC was probably at or below 1%. Even with the range extender running I could only do about 40 mph. 
It's not as simple for the i3 owners that have the ranger extender option, and the majority of people reporting the problem are indeed i3 REx owners. That's because unlike BEV owners, it's not unusual for them to drain their battery way down to only 6.5%, since that's the set point for the range extender to turn on. Because the SME module is slightly misreading the battery's state of health (capacity), the REx is actually turning on at around 1% to 3% while the car thinks it has 6.5% remaining. Once the REx does turn on, it doesn't operate at a high enough output to sustain driving at highway speed because it thinks the SOC is at 6.5%, while the battery is struggling to supply power at less than 3%. In some cases the car will continue to drive along at reduced power mode, but others have seen the car simply slow down and shut off shortly after the range extender operation began. 

In most cases a BEV owner will be very close to their destination when they realize they have the problem, since they only had a few miles of range remaining anyway - or so they thought. On the other hand, REx owners could be many miles from their destination, as they were relying on the range extender to allow them to complete their trip. Either way, it's not a pleasant experience, and I know because it happened to me back in December. I have one of the early 2014 i3s (the first REx delivery in the US, actually), and also one of the highest mileage i3s with over 67,000 miles on the odometer. Luckily, I was able to get home. Since I had heard of others experiencing this issue, I knew exactly what was happening. I took secondary roads home, kept the speed under 45 mph and I made it without a problem. However most other i3 owners aren't necessarily as informed as I am about the car, and they won't understand what's happening or how to mitigate the issue and get to a plug. 

The power bars are beginning to disappear with the REx running and a displayed 4% SOC. That shouldn't be happening, especially when driving slowly as I was. At that speed, the range extender should have no problem maintaining 6.5% all day long. 

I'm recommending all 2014 i3 owners that haven't already had their car reprogrammed, take it to their dealer to have it checked for this problem. Tell your service writer to look up service bulletins B612016 and B612116. These bulletins will instruct the dealers on how to correct the problem. You should also make sure you have software version 16-11-502 or later. in the meantime, if you drive a BEV i3, then try not to let the SOC drop below 8%. If you have a REx, closely monitor the power bars when the REx turns on. If you see any of them disappearing, then slow down and get to a charging station as soon as possible because you can't rely on the REx until this is fixed. If you have a 2015 or newer i3, then I wouldn't worry about this. By the time your car might experience these symptoms, you'll have had newer software updates that will proactively eliminate the problem before you've experienced it. 

Recently, BMW HQ has stepped up their game and has been reaching out to their service centers to make sure they are aware of the issue and can identify it quickly.  Service bulletins B612016 and B612116 have been updated with a new procedure to perform an ISTA capacity adaptation test after programming (This is a new function in ISTA 4.04.3). It should prevent future cases of range extender not turning on when the SOC drops below the threshold. At the very least, this will allow REx owners to get home if they encounter this problem because the range extender will turn on and replenish the battery enough to allow driving. However, so far what I've witnessed is the uptake has been uneven; some dealers are on it, and others are still struggling to identify the issue when a customer comes in. The one thing I've noticed is that when the owner knows the exact issue, and gives the service writer the bulletin numbers, then in nearly every case I've followed it's been fixed on the first visit. Don't let the dealership tell you there's nothing wrong with the car. Forward them this post, if you must. There have been cases where the software update didn't work for some reason. When that happens, the dealership needs to connect the car to BMW HQ and perform a remote IRAP session. The IRAP reprogramming will definitely resolve the issue if the software update doesn't.

I know this because many i3 owners reach out to me for advice with their car, often when there's an issue. In this case, I've had more than a couple dozen i3 owners ask if I could help them out. They have been driving the car for more than two years now, so they know this isn't how it usually works. Yet, when they bring it in for service, often the service team tells them there's nothing wrong. Here's an example of what one service center told an i3 REx owner that had the issue once while driving, and another time when he tried to turn it back on to continue driving:

Hi Xxxxxx,

"It appears that you are driving the car down to a very low charge.  Once it is stopped, the charge is so low that it will not let you go anywhere. They’ve told me that when the range extender kicks in, it does not charge the battery.  It keeps the battery charged to get you another 10-30 miles down the road depending on driving conditions.  The vehicle will reduce power and loads to help get the battery to last a little longer, how I understand it.  But after you reach your destination, the car needs to be charged."

That's just an incorrect diagnosis, and not really a proper explanation of how the range extender works. The only reason the state of charge is too low when the vehicle stopped is because of this problem. Under normal operation, the REx will keep the SOC above the low charge threshold that prevents startup. The fact that the owner can drive it to the point that it won't restart should immediately be a red flag that there's a problem. In the case of this issue, the range extender is actually working properly. Its operation is based on the state of charge. The lower the state of charge, the harder the REx works to produce energy to maintain the SOC. If the car is telling the REx that there's more than 6.5% SOC, than the REx won't turn on. But if reality there's actually less than 1% SOC, then the car won't turn on. The misdiagnosis and improper response to the customer is really a microcosm of the challenges dealerships have dealing with a car like the i3 REx, that operates unlike any other car in production today.
An i3 with the range extender option exposed. The electric motor and power electronics are on the left, with the jumper cables attached. The REx motor is on the right under the black heat shield.
There may be some adventurous i3 owners who want to cheek for themselves if their car has this problem. The only way to test it, is to exhaust the battery and see if the issue appears. The good thing is you don't necessarily have to wait until you're stuck to see if you are about to go into reduced power mode. The ePower display will let you know before it's too late. There are 11 small blocks on the right side of the driver's display screen. (See pictures of the power blocks above) Under those blocks is the word "ePower." As the car begins to go into reduced power mode, one by one the blocks disappear, starting from the top. To test if you have the problem, you want to:

A) Drain the battery down below 7% SOC, and then 
B) Keep driving but watch the ePower gauge. 

If you see the ePower blocks disappearing from the top, before your SOC drops below 3.0%, then you probably have this problem. You shouldn't experience any reduced power with more than 3.0% state of charge. To protect yourself from getting stranded during this test, do it within a mile of a charging station, or drive up a long hill -- you can always turn around and descend to regen some power back into your battery. If you get the battery down to 3.0% SOC with no loss of ePower blocks, then you don't have the issue. To display the battery SOC, tap the BC button on the end of the turn signal stalk and watch the upper left corner of the driver's display. However, even if you don't seem to have the problem, I'd advise having your dealer update your version of software and check the state of health adaptation value. 

Finally, I don't want owners to freak out over battery capacity loss. This is completely normal for any electric car and that's not the problem here. The car needs to properly adjust to the capacity loss over time to give a proper state of charge reading and therein lies the cause of this issue. Once BMW updates the software, there is no issue. As I mentioned above, I have close to 70,000 miles on my i3 now and my battery is nearly as robust as it was when it was new. My range seems just as good as it was in May of 2014 when I took delivery. Perhaps I've lost 4 or 5 miles or range but honestly, I can't tell. BMW has an eight year, 100,000 mile battery capacity warranty for the i3 that guarantees at least 70% capacity. Based on what I've seen so far, I highly doubt that they will have many claims on that warranty, if any. 

Hit tip to fellow i3 driver Chris Campbell for providing information used here, and for prodding me to post about the problem so other i3 owners affected by the issue know what to do.