How it works
Battery life depends on the average current, not the peak. A device that draws 80 mA for 2 seconds every 10 minutes and sleeps at 10 µA the rest of the time averages well under 1 mA.
Real batteries don't deliver their full rated capacity, especially in the cold, at high pulse currents or near end of life, so the usable-capacity setting derates it. 70–85% is a reasonable starting point.
I_avg = (I_active × t_active + I_sleep × (T − t_active)) / T
Life (h) = Capacity (mAh) × usable% / I_avg (mA)Worked example
A 2,000 mAh battery powers a sensor that draws 80 mA for 2 s every 600 s and sleeps at 10 µA. Average current is (80 × 2 + 0.010 × 598) / 600 = 0.277 mA. At 80% usable capacity it lasts 1,600 / 0.277 ≈ 5,780 hours, about 241 days.