RE: E-Starter/Battery problem
If the motor cut out, and you still had control, that means the LVC (Low Voltage Cutoff) feature of the speed control kicked in. There's nothing wrong with the ESC, at least.
~720mAh AAA NiMH cells are at their extreme limits powering a GWS EPS300/350C drive. Brand new, they can't cut it. NiMH cells need a few cycles to really get working. I suspect that this, coupled with the cold, is your problem.
If you can cycle the cells a few times before you go flying again, then you should see better results.
As an alternative, KAN650 or CBP650 cells work much better. These are "2/3 AA" cells that are slightly heavier than AAA, but are much more capable. You can get the CBP650s in custom packs at cheapbatterypacks.com. KAN650s are available from many sources.