Yeah. Just charge it and reset one of the trip meters on the left side display. Open your windows and turn the heat to max. Takes about 3 to 4 hours, when the car dies, you'll know how much battery capacity you have. I think the older FFE had 19-20 kWh originally.
What I do is reset my odometer before I'm going to go on a drive that will use the majority of the range. When I get home (hopefully with less than 15 or so miles range remaining), I roll down the windows and turn the heat to max, and let it run until the car dies. Doesn't take nearly as long, plus means that you haven't just used one cycle of your battery without getting the benefit of driving.
You can also estimate your battery capacity by resetting the trip odometer, driving a certain distance (again, hopefully running the battery down quite a bit), then recording the amount of electricity used. Then, one of the screens in Sync will show a % remaining of the battery. A bit of math, and you can calculate your total battery capacity. I've found doing this results in a bit higher battery capacity; the last time I did that, I got a bit over 17 kWh, whereas the run-down test showed only 16.7.