Call Nightrider on the phone and ask. The phone service is pretty good. Do not try and email them. Some of the lights with multiple settings have problems similar to that. Also can you test it in the house to see if it is the cold? If you do keep a fan running on the light. You could insulate the battery with some kind of foam or an insulated lunch bag and strap a chemical hand warmer to the battery. If the cord is long enough put the battery under your jacket, that works great. I would not expect that much change at 40. Most of the water bottle batteries are held in the bottle by that expanding foam. That also insulates the battery . A battery in a pouch will get cold much faster.