How much capacity do you really have?
I recently bought a Nissan Leaf, and I'm going to share the joys and travails of driving one.
We were going to head out blueberry picking today. Our destination was 34 miles away, and the Leaf claimed it had 80 miles of charge available. "Perfect!" I thought - I could exercise it at its full range, and trickle charge enough overnight to get to work tomorrow, where I can fully charge it.
The first five miles of our trip was uphill on an interstate. By the end of that, the Leaf claimed we had 47 miles of charge left. We turned around, went home, and switched to the Sienna for our blueberry picking adventure.
What happened here? Two things: route selection, and mileage variability. The route selection on the Leaf isn't what I'm used to: on my prior vehicles (Toyota/Lexus), when selecting a route, it would display several options. The Nissan interface didn't, although I'm sure it is there somewhere (something to go look for!). So I had selected the "long but fast route," which added 7 miles, but saved 3 minutes at normal driving speed.
Which leads to mileage variability: 80 mile range is really some number of kilowatt-hours; and different driving has different miles-per-kilowatt-hour efficiency. "Optimal" driving is at 38 mph; the "long but fast route" involved speeds that are at least 50% higher, with a concomitant reduction in efficiency. While 80 miles didn't assume optimal driving, it probably didn't expect such high speed driving.
Feature desire: If you put in a route, and the expected fuel efficiency for normal driving on that route won't get you home on your existing charge, give a warning. This probably requires some better GIS integration, but shouldn't be out of the realm of possibility.