Usable capacity on the 33.5kWh battery is in the upper 20's kWh. I don't know how the car calculates the battery % that shown on the screen but you might check what it says when your GOM says 7km left. If it says you have 20% left then just keep driving until the % drops to single digits. However I would suspect if the GOM is wrong the % shown on the screen could also be wrong. I think with Forscan you can read the battery voltage. If I remember correctly 3v per cell is a dead battery and 4.2 volts is fully charged. I don't remember the exact numbers so the following is approximately what the car does. The car will only charge to just over 4V/cell (90% SOC) so 86 series x 4ish volts = 350V for full pack voltage. An empty pack is 86 series x 3 volts/cell = 258 Volts. I believe the car keeps about a 5% buffer so you should never see a pack voltage this low. I don't know what this translates to in voltage but I'll guess it's probably in the neighborhood of 275 volts. Hopefully someone who has done these measurements can chime in. The pack voltage to capacity remaining isn't even close to being linear so it's really hard to gauge state of charge except when near full or near empty. The point I'm trying to get at is that you can simply use pack voltage guestimate if you are really close to empty with 7 km remaining on the GOM.
2014 Blue Candy FFE
http://www.fuelly.com/car/ford/focus/2014/triangles/303811 (since this forum doesn't allow BBcode in sigs)