Came here hoping to find an answer to a similar question.  I started a rather cold weather ride a few days ago and the motor just stopped about three blocks from my house.  Battery at 80%, all wires connected.  No idea what happened. 

I do store my bike in an unheated garage most of the time, so I figured it might be due to cold.  This has never been an issue in the past, however.  I fired it up after a few days in the house, and the motor seems to work fine.  Still wondering, as I don't want to get stranded on my 13+ miles commute on mostly rural roads.