-13c shouldn't be a problem not plugged in. Got two here, one's a 1.6 with about 420lbs compression. Car will start down to about -20 although it's a lot happier plugged in. Running 5w40. Cycle the glow plugs a couple of times, shove the clutch in (less drag when you're not turning tranny parts in cold oil) and start it WITHOUT! the cold start lever. Pull it as soon as the car fires. As long as the battery is in good shape, (starter, wires etc.) it should go. Get the battery load tested somewhere, maybe get the starter checked for draw too. Keep the car parkrd out of the wind if possible, or at least with the back of the car to the prevailing wind. Lots of good advice about timing and compression, injection here too. Good luck!
Other car has a 1.9, don't know the compression, but I don't plug this one in at all unless the wind chill is -30 or more.