Sizing & runtime
IoT & Sensor Battery Life Calculator
Estimate how long a duty-cycled device (sensor, tracker, beacon) runs on a battery from its sleep current, active current, active time and wake-ups per hour.
Results are mathematical estimates from the values you enter — not measurements and not data about a specific product or vehicle.
How does the IoT & Sensor Battery Life Calculator work?
Battery life = usable capacity ÷ average current. The average current is the time-weighted mean of the active and sleep currents over one hour, plus an equivalent self-discharge current. Units matter: sleep currents are usually in microamps, active currents in milliamps.
Formula
d = t(active) × n ÷ 3600 (duty cycle)
I(avg) = I(active) × d + I(sleep) × (1 − d) + I(self)
I(self) = C × sd ÷ 8760 h
life = C × f(usable) ÷ I(avg)Worked example
2,400 mAh, 5 µA sleep, 20 mA for 2 s, 4 times per hour, 85% usable → d = 0.222% → I(avg) ≈ 49.4 µA → ≈ 41,270 h ≈ 4.71 years.
Limitations and warnings
- Radio transmissions often draw short peaks far above the average active current; measure the real current profile with a power analyser.
- Many primary cells cannot deliver their rated capacity at high pulse currents or low temperatures.
Four values that are often confused
- Nominal capacity (Ah)
- Charge a battery delivers under rated conditions, usually over 20 hours (C20) at 25 °C.
- Usable capacity
- The part of the nominal capacity you can use without damaging the battery — about 50% for lead-acid, 80–90% for LiFePO4.
- Cranking current (CCA)
- Current deliverable for a short time in the cold to start an engine. It measures power, not stored charge, and cannot be converted to Ah.
- Stored energy (Wh)
- Ah × voltage. The right unit to compare batteries of different voltages.