Probably excess battery discharge. Did yours have a battery tender installed at PDI? My dad had taken his 335 in several times and all because the battery was low. They charged it up and sent him on his way. Try charging the battery and do this every night when it gets to be below about -15. Especially because of Winnipeg traffic (all stop and go) the battery never had a chance to really charge.
So before you run out and put in a new battery, try charging it consistently every night and see if that helps.