Monday, December 8, 2014

BMW i3 PSA: No, There is Nothing Wrong With Your Battery!

As the temperatures drop, so will your range. That's life with an electric car, but there are ways to minimize the effects of the cold.
I remember back to my first year in the MINI-E program. It was 2009 and there weren't many electric vehicles on the roads, especially outside of Southern California. About five months into the MINI-E Trial Lease program there was a rush of participants bringing their cars to their MINI dealer for service, telling them something was wrong with their cars. This occurred in late October...

Suddenly, the cars couldn't go as far as we were used to, and the range drop off seemed to happen very quickly, without notice and without reason, leaving many people to assume their car was malfunctioning, and perhaps had a bad battery. Some of the people even swore the range drop coincided with their last service visit, so there had to be something done at the dealership that caused the loss of range. I had read quite a bit about electric cars before getting mine, and knew there would be some range degradation in the cold winter months of Northern New Jersey, but I really didn't know how much the range would drop. Evidently many of the other participants were completely in the dark about what to expect once the winter months arrived. Some were so put off by the range degradation, they insisted that BMW take the car back and allow them to leave the program. I remember one particular person tell me that drop in range meant they could no longer make the round trip to work every day, so the car was of no use to him for three months of the year.
48 miles was all I could muster before my range extender turned on last week. My battery is fine, it's just cold!

When the MINI-E program ended in 2012 I joined the BMW ActiveE lease program. By then some of the participants were aware of the effects the cold weather has on EV batteries since mainstream EVs like the Nissan LEAF and Chevy Volt had both been available for over a year. However there were still quite a few ActiveE drivers who were caught off guard by the loss of range once winter rolled around, and this became a major topic of discussion among the ActiveE discussion forums. Just as with the MINI-E drivers, many believed their car was experiencing some kind of battery problem, and couldn't believe the range would be affected so much by the cold weather.

With temperatures in the low 20's, my predicted range is usually in the low 50's for a fully charged battery.
So here we are in 2014 and not much has changed. The i3 launched in May in the US, and the vast majority of owners have never owned an electric vehicle before. Many of those who live in cold weather regions are now finding out firsthand how much the range can be affected by cold weather. I am the admin in the i3 discussion forum over at and the reduction of range has been widely discussed of late. Just as with the MINI-E and ActiveE programs, there are people who are convinced that there is something wrong with their car. I suppose there could be an issue with someone's car, so I would recommend to anyone concerned to take their car in for service to have it checked out, but I'm sure most everybody is going to get a clean bill of health, and at that point they are going to have to come to grips that the reduced range is due to the temperature, and learn how to live with it.

With temperatures in the 40's, I was averaging 60 to 65 miles of range per charge.
I must say I am a little disappointed in BMW for not offering better educational information for new owners. It wouldn't have been too difficult or expensive to prepare an information card which helped new owners understand how temperatures can effect their range. I've had a couple dozen i3 owners reach out to me already for information about this, many concerned they have a problem with the car. I think BMW should make a "Battery 101" information card and hand it out to all new owners at the time of delivery with their other vehicle documents. This could cover temperature issues as well as tips to help extend the life of their battery, offer advice for long term vehicle storage and offer a brief explanation on how the battery system works. I believe owners would appreciate this kind of information. It feels a little like Groundhogs Day with the same questions about range coming up every winter. There has to be a better way to prepare the customers for this before it becomes a problem.

This range chart is used by BMW for dealer training. It should be incorporated into a retail version to hand out to the customers upon delivery. This kind of information would be very helpful to the end user and often doesn't get passed along from the client adviser. Hat tip to Eric Loveday for reminding me about this dealer document.

That said, there are techniques to help offset the effects the cold weather has on the battery. Here are some of my recommendations to help get you throughout he winter:

Precondition: Use the precondition function as much as possible. The i3 will preheat the battery and passenger cabin so you leave with a fully charged and heated battery, plus a warm cabin. By doing so, you will use less of the stored energy in the battery for these functions, which will allow that energy to be used for its main purpose, to propel the vehicle. You can set the preconditioning to begin every day at a set time so your car is ready for you. Make sure the car is plugged in while you precondition because you want to draw energy from the grid to do this, not drain down your battery.

Cabin heat: Limit the use of the cabin heater as much as possible. The BEV i3s are equipped with an advanced heat pump which is much more efficient than the resistance heater used for the REx i3s. However it still can use a fair amount of energy and will indeed cut into the range. If your i3 is equipped with heated seats I highly recommend using them as much as possible. By doing so you can use the cabin heater less which saves energy since the heated seats use less energy than cabin heater; heat pump or not. If you simply dress a little warmer and use the heated seats you can really cut down on the use of the cabin heat, and this will definitely have a positive effect on your range. If you are wondering why i3s with the range extender do not have a heat pump, there are two main reasons. First and most importantly, the actual heat pump on the BEV i3 is located where the gasoline tank is on the i3 REx, so there isn't room for it. Secondly, squeezing every mile possible out of the battery isn't quite as important with the REx i3, since you can still continue driving once you exhaust your battery. With the BEV i3, those extra 3 or 4 miles the heat pump may add might make the difference in you getting home or not on a cold night. 

Properly inflated tires: Tire pressure falls as weather turns colder. Some tire experts say that for every 10 degrees of temperature drop your tires can lose 1-2 lbs of pressure. Under-inflated tires create more road friction which will reduce efficiency. Some EV drivers I know actually add  four to five pounds of pressure to all of their tires before the winter months begin. Always make sure to check the recommended and maximum pressure for your tires, as that's different for every tire and car. 

Park inside: Whenever possible park the car in garages, especially if they are heated. If you park outside for an extended period like while you work, you should find a spot that will be in direct sunlight for as much as possible. By parking in direct sunlight you’ll have a warmer cabin and battery when you return to your car later.

Slow down: Besides preconditioning and conservative use of the cabin heater, driving a little slower is perhaps the best way to extend your range. This is true regardless of the ambient temperature, but during the winter months driving a little slower can help offset the range you lose to the cold. If you do knock off a few miles per hour on the highway, make sure to move over into the right lane so you don't hold up traffic. Also, try to accelerate slowly form a standstill. Jack-rabbit launches are definitely fun with the i3 but they do consume a lot of energy. 

Charging times increase: While you're charging, the thermal management system will also be working to warm the batteries. This takes some of the energy that would have gone directly into the battery and uses it for the TMS. On really cold days I've noticed it takes my car 30 to 45 minutes longer to fully charge. Knowing this you may have to adjust the delayed charging setting on the car and allow for more time before you can unplug.

Use Eco Pro Modes: The i3 has two Eco driving modes to complement the default "Comfort" driving mode; Eco Pro and Eco Pro+. Both modes reduce power supplied to the motor and energy consuming features like the cabin heater. Most features work fine in Eco Pro mode, but Eco Pro+ restricts the power so much to them that some no longer even function. Another benefit to using Eco Pro and Eco Pro+ in the winter is by reducing the power to the motor the car accelerates slower and helps to reduce the possibility of wheel spin. I definitely recommend using Eco Pro mode whenever driving on ice or snow covered roads.

99 miles of predicted range was the most I have ever seen on my i3. This of course was months ago when the temperatures were in the low 80's. I've never actually been able to drive 99 miles before my range extender turned on though. The most I've ever driven was 90 miles once. I've learned that the Guess-o-Meter can be overly optimistic at times!

Below is an interesting chart prepared by FleetCarma. It compares the effects of the cold on the fuel efficiency of an electric car and a gasoline car. It isn't exactly what I'm discussing here today, but it helps to see how both gas cars as well as electric vehicles are effected by the cold. It's interesting to see that the cold affects the EV more, but the actually energy cost of the reduced efficiency is less on the EV. So while it may be a greater inconvenience for the electric car driver, the cold weather inefficiencies actually costs the gasoline car driver more money.


  1. Great post and info Tom! May I ask 2 questions 1 does the TMS warm or cool the pack when plugged into L2 but not preconditioning?
    2 the 50 miles estimate on your rex before engine start, is that with any cabin heat set, or the cabin heater totally off?

    1. Good question2. The TMS won't actively regulate the battery temperature when the car is plugged in ant not charging. I do believe it will initiate if the battery temperature gets to a critically high or low temperature though, as I was told that a while ago by a BMW engineer but I haven't followed up on confirming it. I wish the i3 had a battery temperature display like the MINI-E and ActiveE did so I could monitor this myself but for some unknown reason BMW didn't include this important feature. I understand the average new EV owner may not see the need for the battery temperature display, but experiences drivers do want it, especially if they live in areas where it gets very cold or very hot. I will continue to lobby BMW to add this display somewhere in the iDrive information screens for those that want it.

      I always leave the heat set to 72 degrees so the range estimate was with the heat and heated seats on. Since I have the REx I don't have to sacrifice comfort for electric miles - the winter was a big part of why I went for the range extender. 50 miles just doesn't cut it for me.

  2. This morning with the 23 degrees out I got 43 miles range with 71% of my battery. I should have been able to get 60.5 miles range. COLD!!!! BRRRRRR!!!

  3. Tom, do you know if preconditioning operates any differently when triggered manually using the Remote screen in the app compared to setting a scheduled departure time? I've seen the suggestion, either on the i3 forum or the Facebook page, that the battery is heated using the scheduled departure time but that only the cabin is heated when preconditioning via the Remote page in the app. It doesn't seem logical.
    (I've reposted this comment/question so that I could edit it.)

  4. So Tom you are quoting about a 50% DROP in range (48 miles vs. 99). Earlier this year you were asked on the forum what kind of drop to expect in cold weather, and you said 20-30% MAX. What gives? Suddenly 50% is the drop and you are fine with it?!

    1. I never said the car has a 99 mile range. The picture above is of the range estimator, which many of us call the Guess-o-Meter because it's just a guess of what your range will be. If you read the caption below the picture I said I've never gotten 99 miles per charge and the most I ever got was 90 miles and that was only once. I average about 70 -75 miles per charge in moderate temperatures. A 30% reduction of that is exactly what I'm seeing now, around 50 to 55 miles per charge. There will always be extreme cases where you get much more miles than the average and much less miles than the average, but overall my average from the best weather to the worst weather is roughly a 30% swing which is what I expected and am fine with.

  5. I also use Rain-X Anti-Fog on my interior windows in my C-Max Energi so that I may reduce the defrost setting on the HVAC controls.

  6. It is hard to keep people with unrealistic expectations happy. It is also hard to keep things into perspective as people tend to dwell on the negatives regardless of how minor they could be.

    I know that personally since I'm often one of those people :)

    Here is another way to look at it:

    The optimist, the glass is half-full,
    The pessimist, the glass is half-empty,
    The engineer, the glass is twice as large as it should be,
    The EV driver, I'll just stop and get a refill ;)

  7. An interesting difference between my Ford Focus Electric, which I just returned after the lease ended, and my new i3 BEV is that the FFE only allowed preconditioning when the car was plugged in, while the i3 allows preconditioning even when its not plugged in. I typically precondition before I drive in the cold even when not plugged in. Then when I start driving keep the heat off and only, if needed, turn on the seat warmer. I was wondering if the net value of preconditioning on both the cabin temperature and battery performance exceeds the cost of having turned on preconditioning when the car was not plugged in. My subjective feeling is that preconditioning even when not plugged in provides some benefit but I have not systematically collected any quantitative data to support this conclusion. Does anyone else know? Does BMW suggest preconditioning even when not plugged in?

  8. I got very knowledgeable info. Nice information. thanks for sharing..!

  9. Very nice article. It's interesting that this cold weather effect has been well-know to people who converted cars to electric for a few decades now (it is much worse with lead-acid batteries). The typical solution is to add some form of heating for the batteries. My converted car uses LiFePO4 cells which I placed on an aluminum sheet with battery heater pads attached to the underside of it inside an insulated battery box. I leave the heater pads powered on when the car is parked in the (unheated) garage at home. They only draw a total of 350W, and are only on part of the time due to the insulation in the boxes. I heat them to 65 F, and they will remain above 50 F for about 5 hours when the car is parked outside in 25 F ambient. As a result I see little difference in range between winter and summer - unless I use the cabin heater as you mentioned. The drive train is also "stiffer" in cold weather so decreases range a bit. I do the things you mentioned, dress warm, park in the sun, seat heater...Sounds like the preconditioning is similar in that it can be used to heat the batteries before you unplug. Manufactures should explain these things to people up front, not in literature they get after they purchase the product, since some may have commutes they cannot make in winter time, and wouldn't purchase the car if they knew that. One of the first questions people ask when considering converting a car to electric is about range. We always warn them range will be significantly reduced in winter if you don't heat the batteries, regardless of battery chemistry.

  10. Where was this information when this car hit the market? If the target buyers were only "electronauts", then it might not be needed. But I am someone who heard about the 100 mile range (,, I learned about the reduction to 80 miles deep in the purchasing process and decided to go through with it anyway.

    I appreciate the in-depth coverage of this issue now, but wish I had been warned that the usable range would be 40-50 miles during the winter. My work and the places I frequent have not changed, but with 30-40% reduced capacity, my life sure has.