I use a green laser pointer at night to do astronomy related work. I got a cheap $5 green laser pointer off of ebay, and when it's a warm summer night, the device works fine. However, the second it touches the cold, it fizzles out and gives me almost zero output. My idea was to use a thermistor with a positive response curve, that is, as the temperature goes up, the resistance goes up as well. When it is cold, resistance is low, and current flows through the thermistor, generating heat, warming the batteries and diode. As it warms up, the resistance increases, diverting current do the now warm diode. I realize this design is not without its flaws. Does anyone have any suggestions?