Today, I did a quick flick of the key to wake up the ignition system, then turned it off before turning the key again. It started up immediately without any struggle or straining noises. Is this something I should have been doing all along to help protect the battery?
Whatever works. If hanging a black feather from the antenna made it go better, that's what I would. One thing about lead - acid batteries; they tend to recuperate if they are allowed to stand for awhile. If it sounds like it is weakening, go inside and let it rest for 10 or 15 minutes.
Ceili cites one problem at -44C. Keep in mind that at minus 40, both thermometers are the same, so - 44C is really, really cold. I haven't had a problem with ice forming since 1970, and that was a cold winter in northern Illinois.
Diesel, and probably gasoline are blended differently for cold weather. If your last fill up was in warm weather, you might be running the wrong blend, so I would go ahead and fill it now.