How do I calculate battery life allowing for duty cycle?
If it's a duty cycle of 4%, then the average load is 4% of 1.95mA, or 78 uA.  The battery should last 2610 / 0.078 hours, or 33461 hours.  Over 3 years.

Battery capacity changes with temperature, time, and discharge rate (and the 2610 mAh rating isn't too precise either, in my experience.)  These calculations are probably within ±20% of the real answer.