I usually flash the car with the Cobb AP in the summer without the battery charger. I unhook the fan so it doesn't run. It usually takes about 2 minutes or so. I don't think the Cobb AP draws that much power from the battery to drain it. (I could be wrong?)

I know the battery performance is lower when its colder outside. What would be the best way to flash the ecu in the cold winter months? Use a battery charger?

 

I don't think its needed. I flashed my car a ton of times warm or cold. No ill effects.