This is a re-post from another thread, but it really belongs here.
Actually, I realized that by doing a little algebra with the stated battery times with and without the radio, I can arrive at the answer.
Battery life for 2700 mAh NiMH batteries with 1 pulse/minute at -20C (-4F):
No Radio: 57h (from manual)
Radio at 10 mW: 28h (from manual)
Radio at 25 mW: 16h
Radio at 50 mW: 9h
Radio at 100 mW: 5h