According to the manual, the key batteries deteriorate within 3 ft of cell phones, computers, and even table lamps. Sheesh! I'm nearly always within 3 ft of one of those. Maybe I shouldn't read the manual after all...
Regardless, the battery is constantly being depleted while driving much different than your fathers Oldsmobile with the fob that just opened and locked the doors. Im changing the batteries after two years as preventive. Five minute job and the battery cost is negligible.