Though she never really tries
I probably should have titled this post 'Do not trust your Guess-o-Meter' aka the estimated remaining range the i3 displays. It might have gotten more readership if I had, but I do have a schtick to uphold with these blog posts.
After 2.5 years, three BEVs and what some might say is an embarrassingly low 30k total electric miles, I'm here to tell you that no one with significant seat time in any of the current production BEVs relies on the guess-o-meter (GOM). OK, no one might be a bit too strong, but you get the point. The fact is, the GOM has no way of being very accurate - best case they are running an algorithm that can accurately forecast total range based on your prior driving efficiency - but my experience says even that isn't remotely close to being true. Either that or EV manufacturers need to develop much better algorithms. Beyond that, the car has no way of knowing how efficiently (or not) you will drive going forward, so you really shouldn't expect it to be accurate.
Our i3 GOM typically indicates 65-75 miles when its fully charged - even after I've averaged 6.5 miles/kWh for the past week or so of driving. For those not doing the math at home, 6.5 miles/kWh works out to over 120 miles of range, yet the GOM routinely indicates 70 or so.
The GOM is actually so inaccurate that even with 75% of the available battery capacity depleted and 90 miles driven it will indicate that I've got less than 10 miles of remaining range even though my efficiency history from that trip would say that I've got 30 miles left.
So what's the take away message here? While I said above, 'Do not trust your Guess-o-Meter', I'll say it even stronger here - don't even bother to look at it, it is not accurate, and will, in all probability cause you stress.So what should you do? The most help I can be is to tell you what I do - maybe it will work for you, maybe it won't. But to get a real sense of the vehicle's range you need to treat it like you would have if it had a gas tank, a gas gauge and a trip odometer. How many people rely on the mileage GOM in an ICE (for those cars that actually have them)? I'd venture a guess that it's not many. So do something similar with your BEV.
Here's how I monitor range when I've got a trip that will test the range of the car.
- Reset the trip computer every time you charge to full
- Monitor the following throughout any trip
Average Efficiency - 4 bars of remaining capacity
- Average Efficiency for the trip
- Real Time Efficiency
- Perform the calculations in your head while driving
Which calculations you may ask? Here's an example:
- You're taking a 110 mile trip
- You've just 'used up' the first of the four bars of capacity.
- Note that your total usable battery capacity is 18.8 kWh and each bar equates to 4.7 kWh.
- Current trip efficiency is at 5.2 miles/kWh and you've traveled 24.5 miles.
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| Battery Depleted |
How do you know if you're going to make it? At this point, you won't. With only 24.5 miles traveled and 25% of your capacity used, you're only going a total of 98 miles at 5.2 miles/kWh.
So what do you do?
- You're going to need to increase your efficiency so that you average almost 5.9 miles/kWh for the entire trip
- Which means that you're going to need to average 6.1 miles/kWh for the rest of the trip
- The difference here is significant enough that you're going to want to monitor your real time efficiency
- Why? Just monitoring an increase in the average won't tell you if you'll make it until either you get to that 6.1 average, or you're stranded
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| Real Time Efficiency & Battery Capacity |
Can't run the numbers in your head? This is where a passenger with a smart phone comes in handy - they can continually check to see if you are operating at the appropriate efficiency to complete your trip.
Hopefully you find how I monitor my achievable range helpful, but even if you didn't, don't stress about the GOM projection. Like America sang, 'She's a Liar - she never really tries'. And if you can't seem to ignore it, try a small piece of electrical tape...