Battery Capacity Loss Is Nothing to Fear

It's my belief that electric vehicle manufacturers need to confront the issue of battery degradation head on and explain to perspective customers what they should reasonably expect from their battery pack. There are a lot of external factors that will influence the batteries performance and life span, and some can be controlled by the owner. The best way to deal with the inevitable battery capacity loss and reduced range is to offer the customer tips on how to properly care for their battery pack as well as providing a fair, yet robust battery warranty. It's a simple fact battery powered cars slowly lose battery capacity and thus range, but how much and how fast? This is an important topic and I wrote a post for BMWBLOG on this recently. I received a lot of questions about it (which is good!) so I decided to put the post up here also. The more people it reaches the better...

BMW is on the precipice of stepping into the future of personal mobility. The electrification of the automobile is inevitable; however the question facing the industry is when should they jump in and bring an all electric vehicle to market. BMW has decided the time is now.

Nissan was the first to bring a purpose built, all electric car to their showrooms a few years ago and have sold over 50,000 LEAF’s worldwide so far. While I applauded them for taking the lead and acting at a time when others were still talking about EV’s, I was also critical of their decision to exclude a sophisticated thermal battery management system which would help maintain a consistent range throughout varying ambient temperatures as well as help extend the battery’s life. This omission has proven costly to them as some LEAF customers that live in hot weather climates like Arizona have experienced unacceptable battery capacity loss; prompting buybacks, battery replacements and has even forced Nissan to change their battery warranty to now include capacity loss.

I’ve been in BMW’s electric vehicle Trial Lease Program for nearly 4 years and have driven 120,000 all electric miles. I have carefully recorded data from every trip I have taken and have over 2,400 log entries. I have been monitoring how the battery reacts to factors like speed, ambient temperature and the topographic conditions of my journey, but I have been paying the most attention to how the battery pack has degraded over time.

The battery in any electric vehicle is the most important and expensive component of the car. Electric vehicle battery packs are susceptible to the same capacity loss as any other battery, whether they are used for your laptop or a flashlight. Once you’ve used them for a while, they are never as good as they were when they were new. When people ask me about my ActiveE’s range, rarely do they ask what will the range be in three years – but they should. I don’t think most people that are considering an electric vehicle fully understand this. Take for instance my ActiveE. The official EPA range rating was 94 miles per charge, which is about what the 2014 i3 is expected to deliver. When I first got it I was able to average about 96 miles per charge in moderate temperatures. Fifteen months and 1,000 recharges later, I can expect about 90-91 miles under the same conditions which translate to about an 8% reduction in range. My results are a bit extreme because I drive much more than the average person. In fact, I have 45,000 miles on the car after only 15 months and have charged it over 1,000 times. That kind of mileage would probably be typical after about 2 ½ to 3 years of driving for the average person so I’m sure I have brought on the battery capacity loss earlier than what should be expected under normal circumstances, but it does offer insight into what perspective i3 customers can expect over time.

My data shows I've lost about 2kWh's of capacity(8%) on my ActiveE's pack so far. That isn't bad for 44,000 miles and 1,000 recharges.

The ActiveE has a 32 kWh battery pack but BMW claims only about 28kWh’s are usable. The remaining 4 kWh’s are kept as a buffer because it’s not good for lithium ion battery’s to fully charge to 100% or to allow them to be completely drained. When the car was new, I was measuring on average about 27.4 kWh’s available to me and now that number has shrunk to about 25.25 kWh which is about an 8% capacity loss. Battery capacity loss isn’t linear so it’s not possible to accurately predict future loss. There are also many factors that will affect the degradation that I can control, which further complicates the process of estimating future results.  Since the ActiveE is purely a test car, and will be decommissioned after my two years with it, I don’t have to be really concerned with protecting the battery to help it last longer, but if I did there are some things that I could do to help fend off early capacity loss.

How to guard against early capacity loss

1)    Avoid deep discharges. As mentioned above lithium ion batteries do not like to be frequently fully drained. Once in a while won’t hurt, but you don’t want to be rolling into your garage every night with the state of charge under 5%. 

2)     Don’t leave a fully charged EV sitting unused for long periods of time. While charging to 100% daily isn’t really a problem, if you are not going to be using the car for a while, like days at a time then it’s best to leave it at about 80% charged. A typical example would be if you were going away on vacation for a while. In that case, don’t fully charge the car before you leave. It would be ideal to leave it between 70% and 80% charged until you get back. 

3)     Avoid excessive fast charging. The BMW i3 will have the capability of charging on a DC quick charger which will charge the battery to 80% in about a half hour. While the batteries are not damaged by quick charging process, they can be damaged by the heat created by fast charging. Unlike the Nissan LEAF, the i3 will have a complex thermal management system that is liquid based and its sole purpose is to keep the battery at safe operating temperatures to prolong the battery life and extend the cars range. This system will definitely allow you to fast charge more often without damage than if the car didn’t have it, but most industry experts still warn against consistent use of fast chargers. The science hasn’t really proven this one way or the other just yet, as DC quick charge is just beginning to be available to EV’s, but I would prefer to err on the side of caution and only use DC quick charge when I really needed to. I’m sure a few times a month won’t have any adverse effects.

4)    Don’t leave the car parked in a hot parking lot in direct sunlight if possible. I’m not suggesting you constantly hunt for a shaded paring spot when you run to the shopping mall, but if it is an extremely hot day(90+ degrees) and you’ll be leaving the car parked for many hours, it would be wise to find a spot where the car isn’t baking in direct sunlight. One of the biggest enemies to the li-ion battery cells is heat. The ideal temperature for the battery is 68 degrees Fahrenheit and as the battery temperature rises to about 90 degrees the cells begin to degrade. Once the battery temperature exceeds 105 degrees there is definite cell damage and capacity loss. I have only witnessed such a high battery temperature twice in my ActiveE since the thermal management system is constantly working to cool off the batteries when it’s hot out. I suspect the i3’s thermal management system will work even better since it’s been engineered and refined for about four years now, and the ActiveE’s system was only designed to be used on a short-term test car. In fact, if you look at the above graph you can see a period where the capacity dropped rapidly. That period was immediately following the summer of 2012, when I experienced my highest battery temperatures. I can’t say for sure whether or not that is directly related to the rapid capacity loss, but I do suspect it played a role.

5)    If you don’t need all the range the car can offer on a daily basis, then don’t fully charge it every night. I know above I said it’s not a problem for daily use, however if you don’t really need to then it’s better not to always fully charge to 100%. I may be nitpicking a bit here and others may say it’s not a problem, but if you know you only drive 30 or 40 miles a day commuting, then there is no need to fully charge your EV if it has an 80 -100 mile range. You can set it on a timer to stop charging before it’s fully charged or use the feature that many EV’s have which allows you to set the amount of charge the car accepts. You can charge to 80% daily and then set it to fully charge on the occasional days you need more range. I wouldn’t really worry too much about doing this, but if you are a low mileage driver, then it certainly won’t hurt.

What I Believe BMW needs to do

Capacity loss is a fact of life when you have an electric car, I’ve witnessed it first hand and have the data to back it up. However I wonder if the average prospective BMW i customer understands all this? Probably not. How BMW educates the customer will play a crucial role in their long term product satisfaction. The customer must know what to expect before they buy the car or they are surely to be disappointed a couple years down the road when the destinations that they used to travel to are suddenly out of range. I know capacity loss is a moving target and there isn’t any way to offer exact predictions, but it is possible to produce charts and graphs that will offer estimates for the owner so they are at least prepared for what is to come. I’m sure BMW has much more sophisticated capacity loss data than I do and they can certainly prepare a “Battery 101” brochure for prospective i3 customers so they can learn about this before they buy the car and will be prepared to take better long term care of their battery.

Secondly, BMW needs to show confidence in their product and offer a robust warranty that not only covers defects, but also guarantees battery capacity. GM and Nissan both came out with strong 8yr / 100,000 mile warranties for their EV batteries, and Nissan recently added a capacity loss warranty after their recent problems. Nissan now guaranties the battery will be greater than 66.25% of its original capacity for 5 years or 60,000 miles. I see this as a step in the right direction for Nissan, but I am hoping BMW shows even more confidence in the i3’s battery. I would like to see them guarantee 70% capacity for 5 years or 75,000. I think this is a reasonable offer considering BMW will be utilizing a state-of-the-art battery thermal management system to help maintain proper temperature. Plus being a premium manufacturer, I believe their customers expect a premium product to have a warranty that instills confidence, especially since this will most likely be the first electric vehicle that virtually all of them purchase. A strong warranty may be the deciding factor in whether or not they are willing to take that leap into e-mobility. 

Battery Capacity Loss: The Public Needs To Know What To Expect

The battery pack of the i3 is comprised of eight modules like you see here. Each module contains twelve cells. They are the same chemistry and come form the same supplier (Robert Bosch Battery Systems, formerly SB-LiMotive) as the batteries used in the BMW ActiveE

Anyone who has a cell phone knows that after you've had it for awhile the battery doesn't last as long as it did when it was new. The same goes for electric vehicles. The problem is in most cases it's easier and faster to recharge your cell phone then it is to charge your EV during the day if you need to use it more. Until public charging infrastructure becomes ubiquitous and battery technology improves where we can have affordable EV's that cover hundreds of miles on a single charge, people are going to need to squeeze out as many miles as they can from their EV. Losing 20%-30% of the car's range in four or five years may make the difference in being able to use the car for your daily commute or not.

So what should you expect from your battery after a couple years? I don't think most people know and that uncertainty will keep many from taking the plunge and purchasing their first battery electric car. The answer is information. Manufacturers and dealers need to step up their game and provide this information. The customer has to feel comfortable about the purchase or they won't make it. Worse yet if they buy an EV and then it doesn't live up to their expectations because they weren't informed about battery capacity loss.

I wrote an article for plugincars.com on this topic recently. Rather than write a new post here on the same topic, I'd like to direct anyone interested to my plugincars.com post. Just click on the links below. I am also working on a more comprehensive battery capacity loss post that I'll put up here soon.

Plugincars.com: Electric Car Dealers Must Address Concerns About Batteries

One Year ActiveE Anniversary Marked By Meet-Up's On Both Coasts

I hosted the East Coast meet at my restaurant in Montclair, NJ

To mark the one year (and midway point) of the ActiveE field trial, meets were organized on both the East and West Coast on Sunday, April 7th, by some of the Electronauts. Here on the East I put together the event and out in California a few people including Jack Brown, Andre Deocares-Lengyel and Mariel Knoll did so. The East Coasters met at my restaurant in Montclair, New Jersey and out West they met at the Blue Skye Coastal Cafe. California is such a big state it's really difficult to have only one meet and allow for everybody to make it. On the East most people could get to my place on a single charge, except really for the Electronauts in Massachusetts and Connecticut. I did have someone come from Connecticut which was a 312 mile round trip and as always Don Young made the trip from Shelter Island, NY which is about a 140 miles each way. I appreciate everyone who came, but especially those who drove hundreds of miles and had to stop along the way for hours to recharge just so they could be here.

The ActiveE cake!

We had 15 ActiveEs come, as well as a brand new Model S, a Honda Fit EV, a Tesla Roadster, a Mitsubishi iMiEV and a Zero electric motorcycle. The weather cooperated and was clear and even made it up to 60 degrees which is actually cool for this time of the year, but lately we have had much colder than normal weather so 60 degrees was definitely a win for us. I ordered a custom cake that was made in the shape of an ActiveE and it was a big hit. We met for about two and a half hours and talked amongst ourselves as well as to curious onlookers who stopped by to check out the cars.

We even had three representatives from BMW's ActiveE technical team come and join in. BMW always sends representatives when we host these meets and it's really appreciated. While they can't offer privileged technical information, they are able to answer questions about service related problems and such. At one point they even pulled out a computer and hooked up to one of the cars to download information saving the owner a trip to his dealer which made his day. This kind of participation is really great.

The West Coasters: Photo by Joel Bartlett

Out on the West Coast they met for brunch and some good photo-ops before heading out. Most of the people who went had traveled well over a hundred miles so they had to make stops along the way to charge. At least one dedicated Electronaut drove about 500 miles for the round trip and had to leave the day before just to make it. That just proves California is just too big and we really need to chop it up into three states! ;)



One thing that was said frequently was how it's hard to believe the program is already half over and many don't want to think about giving up their ActiveEs. This all sounds too familiar to me. I can remember lamenting over the thought of giving up my beloved MINI-E but then the ActiveE came along and helped take the edge off turning it in. Will the i3 offer that same relief? I suspect for me it will but many of the others at the meet aren't 100% convinced yet. The non-traditional BMW styling and the lack of much information on the car even as the launch is less than a year away has many Electonauts wondering what their next move will be. I think if the i3 does deliver the same or better range as the ActiveE (94 EPA range rating) then many will transition from the ActiveE right into the i3, but the range is on everybody's mind now. The fact that the battery is so much smaller than what we have in the ActiveE has many concerned, even though it's a much lighter car. On a day like today when people were driving long distances to get together the need for range and a robust infrastructure really stands out.

The ActiveE East Coast team

It's All About The Range....Extender

Now that I have the added hardware, I've re-badged the car as well. 

One of the differences in the MINI-E and ActiveE trial lease programs is the ActiveE lease is more of a traditional automobile lease, where the MINI-E lease was specifically crafted as a beta test program and there were very strict rules. We were not allowed any modifications, we even had to get permission if we wanted to tint the windows. One person was actually thrown out for adding a simple modification that BMW didn't approve of. Now with the ActiveE, we can basically do what we want to as long as we return the car in good condition, and undo whatever modification we have done. Of course we can't do anything that is unsafe or that would be permanently installed so that you couldn't uninstall it, but short of that we pretty much have the green light to have fun.

You can see how much room is up there

I like that BMW is going to offer a small gasoline engine as an option on the i3 to extend the range. It won't be something everyone wants, but those that do can now buy the car without worrying about ever running out of charge and getting stuck somewhere. It will also help in the winter months in cold climate areas where the range drops and make it possible for the owner to complete trips that they wouldn't  otherwise be able to. I've been kicking around the idea of installing a small gas generator to my ActiveE for a while now, basically for emergencies but also for those occasional days where I need a little more range. I then stumbled on a small affordable generator that looked like it would fit perfectly in the empty space under the hood of the ActiveE, in between the front battery block and the fan. It's basically a huge empty space up there, big enough to fit a small suitcase.

The manual is a must for any modifications

So after I confirmed the dimensions would work, I picked up the Ryobi 2200 generator and the project began. Everything was very straight forward, the unit fit perfectly in the space up front and all I had to do was secure it so it wouldn't bounce around and damage anything. The only hard part (and it wasn't really hard) was I had to connect it directly the the KLE(onboard charger) above the power electronics and motor because if I didn't the car wouldn't run while it was charging. There is a safety feature in today's electric cars that don't allow them from turning on if it's plugged in, whether or not it's charging. By circumventing the whole J1772 charging port and connecting the power supply directly the the onboard charger, the car would start and run while it is charging without any issues. I happen to have the full technical manual for the ActiveE so this was not a problem. In fact, I offer the manual for sale on my ActiveE Modification website. It's $19.99 and can be downloaded directly from the site upon payment. The manual is a must for anyone that wishes to modify their ActiveE.

Running the feed from the generator to the KLE

I'm not going to show detailed pictures of the completed set-up or offer instructions on how to do this because I'm concerned about liability(and BMW coming after me for instruction people how to modify their cars) but if somebody is really serious about doing this then contact me directly and I can offer advice on what not to do. All you really need to do is run your supply line from the generator to the KLE and figure out how to connect it. It's literally a three hour job if you know what to do.

I had to install a carbon monoxide detector

I've had it installed for about a month now and it's been working perfectly. Since it's a small generator, it only adds about 6 miles of range per hour. It helps, but certainly doesn't allow for continuous driving. What it does do well is charge the battery while I'm parked for a while. If there are no chargers around and I go shopping or to a movie I can just leave it running and it will charge the car up. That has two minor problems though. First, it's really loud! People walking by really stop to try to figure out why the car is running and way it's sounds like a lawn mower. Secondly, I didn't route the exhaust out anywhere, figuring it would just escape through the seams and underneath the car. When it's on while I'm driving it's no problem, but if I leave it charging while the car is parked for a while, the cabin does get infiltrated with a fair share of fumes. Just to be safe, I installed a carbon monoxide detector inside the cabin so I can monitor it. It is quite startling when it goes off as it's only inches from my head but all I need to do is open the windows for a few minutes and it shuts off. 

Running the genset before permanent install

It really is doing exactly what I had hoped. By running it for a couple hours while the car is parked I can easily drive 110 - 120 miles per day. I know it's kind of cheating using gas and all, but sometimes you just need a little more range. I wish I had this last year when I ran out of charge a couple miles from my house and had to plug in at a Burger King and wait there an hour! Now that I've conquered this I've begun to experiment with a larger generator, one that could add 20-25 miles of range per hour. Of course this large of a generator wouldn't fit under the hood, and would need to be towed on a trailer behind the car but would allow for much longer drives if I wanted to. So I went out and bought a big generator and began to tinker with it. Surprisingly it didn't work instantly like the smaller generator did and I'm not sure why. I even broke out some EVSE's to test the generator charging the car and using a (supposedly) wall mounted EVSE. It got even more interesting when the ClipperCreek EVSE wouldn't charge the car but if I hooked it up to an AeroVironment unit it would. I'm still working on this but I'm sure I'll figure it out. Then all I need to do is get a small trailer to pull the generator. I've already welded a tow hook to the frame of the car behind the rear bumper so it's good to go.

Testing the larger genset with two EVSE's

I figure I'll have this done in a couple weeks and will do a post on it along with video of me driving the car with the trailer and the generator running. Feel free to post questions and comments below but please don't ask me anything specific about installation here, I can't post that publicly. Below are some assorted pictures of the REx experiment:

The ActiveE trunk once you remove the carpeting. The KLE is directly behind the shiny metal door in the center. You simply remove the eight Torx screws and it's sitting right there to connect your supply to.

Snaking the yellow cable from the engine bay to the KLE took the most time. I used a heavy duty 10 gauge outdoor wire and made sure it didn't interfere with anything. 

When I connected the large generator directly to the KLE I used a very heavy gauge high voltage outdoor cable. I'll eventually route this under the car up into the power electronics area before attaching the trailer.

The lighting isn't good, but this view is looking up into the motor assembly. I routed the cable up through here.

The tow hook is ready to go, all I need is a trailer now!

The REx tags are all over the car. If you got it, flaunt it!

UPDATE: For those that haven't figured it out yet, this was an April Fools post. I haven't added a range extender and I don't have an ActiveE modification website. I hope you all had fun with it - be well!