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...