Tuesday, July 13, 2010

35,000 hard miles: No reduction in range yet

It's been thirteen months now that I've been driving MINI-E #250 and I just passed 35,000 on the odometer driving home from work last night. Long gone are the days that I would worry if I could make a destination, if the car had it in it to make a certain range. Once I had the car for a while and I understood it's range and the relationship between speed and range, I very rarely have to wonder if I can make a particular destination. Recently I started thinking how I haven't noticed any reduction in the cars range yet, but I wanted to take a quick look at my trip logs to make sure. If there were any reduction that I didn't notice myself, it would be there in the recorded numbers for me to see.

I drive the car hard, I don't pamper it at all. Actually I drive it harder than if I owned it because after all, I don't own it and I get to hand the key's back to BMW next June and I'm really not responsible for the condition the car(or the batteries) are in. One of the first thing I looked at was how many times I charged the car since I picked it up June12th, 2009. That would be 623 times in 396 days. Since I charge at work, many days I plug in when I arrive at work even if I don't need the extra juice, just to top it off. This was especially true in the cold winter months when I plugged in just to help keep the batteries warm. I also noticed that I plugged in when the cars state of charge was at or below 5% 52 times. I mention that figure because it is commonly accepted that deep discharge is not a good thing for these lithium ion batteries and below 5% would qualify as deep discharge. Additionally, 52 times in 13 months would also definitely constitute "abuse" and I would not want to do this if it were my $25,000 battery pack. You should know, although I keep talking about how I'm abusing the car, I'm not driving it hard to be spiteful or malicious, I'm test driving this prototype vehicle to find the problem areas and help BMW recognize what works and what need to be improved so I'm doing exactly what they want me to do with it; beat it up and find the weak links.

So, after taking a thorough look at 35,000 miles of trip data I can conclude there has been no recognizable reduction of range, even though I have charged the car way more then would be expected in 13 months, driven about double the miles you would normally drive and had frequent deep discharges of the battery pack. The only pattern to range reduction I can see is temperature related. Both extreme heat and cold weather cause the range to drop. I believe it's primarily due to the extensive use of the heater and the air conditioning because they both use a lot of energy, however the extreme ambient temperature does have it's own direct effect on the batteries also.

So thirteen months in the car is still performing as well as it did when I picked it up. It will be interesting to see it this continues or if the excessive driving and charging that I do with the car starts to get the better of it. Stay tuned...


  1. this is good news. I was wondering this very thing the other day when I was reading your blog about the 4th of july. With how much you drive & charge the battery I would assume you will see some degradation at some time, especially if you continue to drain the batteries as you report you do. I think BMW & mini must be very pleased with you. you have been testing the car very efficiently for them. maybe they suprise you and let you keep it ;)

  2. How about the power? Does the car accelerate as quickly as it did when it was new? Also, when it is cold or very hot does the power diminish? How about when you are close to the end of your range

    Thank you

  3. Nice entry. BTW, who takes the great pictures of you in your MINI E (like the one with this entry)?

  4. Christof,

    Some of the pictures I use here (the good ones) were taken by professional photographer Peter Rigaud from Vienna. BMW commissioned him to take pictures of me and the car that they used in their 2009 annual report(There's 4 pages of just me in there!)Anyway, Peter gave me access to the pictures that BMW didn't use for use on my blog. I can't sell them or use them for commercial purposes, but I can use them here which was really nice of him. He was a real pro. You can see his website at:

  5. I bet if you continue to drain the battery so much you will start to see a degradation by the end of the year. These Li-ion batteries cannot survive long with deep discharge.

    Do you know the operating range that BMW has set for the usable battery range, i.e. 20% to 90% or something like that. GM has set the Volt's battery to only operate from 30 to 80%, meaning it will only use 8kwh of the batteries available 16kwh in order to extend the lifespan of the batteries. They have to warranty the pack and BMW doesn't because these cars will be gone before they reach 10 years or 100,000 miles (although the way you drive you might get close to 100,000!)

    Michael Pachek

  6. Michael,

    I think the MINI-E batteries can have an operation range of 10% to 90% of the batteries total energy. The pack is 35kwh but only 28kwh is usable so that is 80%.

    You may be right and I will see a drop in range sometime before I return the car next June, but I bet BMW will be happy if that happens because I would have found the threshold of abuse that these batteries can take. Of all the trial lease participants I have the most miles by far and I'm sure they care carefully analyzing the data downloaded from my car when I bring it in for scheduled service.

  7. These cars seem to be holding together very well especially when you consider they are only test vehicles that are not intended for production. Have you had many mechanical failures so far?

    I think they should figure out a way to reconfigure the battery so there is some more space in the cargo area even it is still only a two seater and sell them.

  8. e-cars are only beginning to realize the potential of battery compositions. We will see a vast improvement in the next years. Prices will drop and performance will advance. BMW & Dailmer will compete with luxury e-car models by 2015

  9. Aubrey: No I haven't had many breakdowns. Twice the car needed to have battery modules replaced and one other time I hit a pothole and damaged the front end. I agree about the selling an electric MINI. The now roadster they are building would make an awesome EV.

    Yes, battery technology will continue to improve. Competition amongst the big auto makers is a good thing, we get to reap the benefits of better products at competitive prices. I'm not sure hat Dailmer has planned as for pure EV's other than the Smart ED though.

  10. Did BMW give you some kind of limit to the amount of charging or miles you can do with the car? How long do they plan on keeping these e cars in service?