I live in Minneapolis, MN and it gets cold here. Really cold.

About two weeks ago, on one of the coldest days of the season (-15 w/ no wind chill) my MINI broke down on the freeway going about 70. It had all the symptoms of a dead alternator...lost power, gauges went haywire and would not start once I finally pulled over. I had it towed home and it sat for 2 weeks until I could find the time to change the alternator.

I went outside today (About 40*) and it fired right up...drove fine.
WTH!?

Could it be possible that the frigid air temporarily shocked or disabled the voltage regulator on the alternator? Should I just replace it anyways? I have the alternator. Just seems weird...and I F(*&$@! hate the MN winters, just a side note.

Also, A shameless plug for 'MINNE MINIs' if you're in the area and have one! Thanks guys!

 

Since there cars are cold tested and sold widely in places like Scandinavia and Canada....
I would look at something other than it was "cold"... Heck it was RUNNING.....even in the Arctic, a car of most any make will stay running once started...
What exactly did it do when it failed...
Any symptoms of an overheat? When the crank pulley starts to slip (common on a s) it will slip and grab alternately...the rubber between the metal parts fails....and it slips under load...
The denso s alternator is the typical design used on most Toyotas and Hondas... So doubt it was just " cold"...the non s valeo is not quite as well built...
Look at the grounds? Tight and clean? The one on the engine mount under the hood can be an issue.

 

My Scan Gage says that the system voltage goes up with colder weather. In the summer it will read 13.5v and when it is 0 deg out it will read 14.6v.

A few other things would be good to know...what year is your mini? Is it a stock MINI battery? When was the last time you had the serpentine belt replace?

What you described is exactly what happen to my '07 MINI when the belt broke at about 10 deg in the middle of a snow storm. Gages went crazy and then the car died.

I would replace the belt, the battery if it is a MINI battery (mine have only lasted 2 years) and get a Scan Gage so you can see what is going on with your car.