I was flying today to try out a new battery. I also had 2 other batteries that were left in my bag in the car. The new battery was recently charged indoors so it worked fine but when I took the first of the batteries that was in the car I got a warning message that the battery temperature is below 25 degrees celsius. It was at 15 degrees so I flew up and flew around in circles to bring up the temperature. I played around with speed a bit and it didn't go very fast so the new firmware is working. At around 22 degrees or so I brought it up and it got to 25 degrees when I got up to 400 ft. It flew fine. I guess to avoid this you should have your batteries indoors or in your jacket or somewhere not too cold. I'm in the Pacific Northwest so it's not really cold around here but it was probably in the low 40s today.