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Battery Life Estimator Spreadsheet

The estimator computes the usable energy from the battery’s capacity and voltage, applies an efficiency factor to account for charge‑discharge losses, and divides by the average power draw over a complete duty cycle. Average power is the weighted sum of active and idle consumption based on the duty‑cycle percentage. A safety margin reduces the resulting life to reflect real‑world degradation and conservative design practices.

Total capacity in milliamp‑hours (mAh). Common values range from a few hundred to several thousand mAh for Li‑Ion cells.
Nominal voltage of the battery, typically 3.7 V for single Li‑Ion cells.
Average power draw when the device is actively performing its function.
Average power draw in low‑power or deep‑sleep mode.
Percentage of each cycle that the device remains active (0 – 100).
Conversion efficiency for charging/discharging and cell losses, usually 80‑95 %.
Margin to subtract from computed life (in %). Recommended 5‑20 %.

What it is

The Battery Life Estimator calculates how long a Li‑Ion or other rechargeable cell will power an IoT device based on the battery’s capacity, voltage, and realistic power usage patterns of the electronics. It models real‑world behavior by weighting the active-state power draw against the low‑power sleep state according to the specified duty cycle. An efficiency factor accounts for round‑trip energy losses in charging, while a safety margin conservatively reduces the projected runtime to leave headroom for temperature or aging effects. The tool outputs the expected life in hours and days, giving makers a quick offline estimate that informs component selection, power‑management design, and prototype testing schedules.

How to use it

Enter the battery’s capacity (mAh) and nominal voltage (V). Provide the average power consumption when the device is active and during idle or sleep modes. Specify the duty cycle as a percentage of each cycle the device stays on; for 10 % active time, enter 10. Set an efficiency value (typically 85‑95 %) to reflect charge‑discharge losses and choose a safety margin (5–20 %) to buffer against real‑world wear. The calculator displays the estimated life in hours and days—use this to compare component choices or verify that a prototype meets its power budget.

Worked example

1. Compute usable energy: 2000 mAh ×3.7 V = 7400 mWh → ÷1000 ⇒ 7.40 Wh. Apply 90 % efficiency: 7.40 Wh ×0.9 = 6.66 Wh. 2. Averaging power over a cycle with a 10 % duty cycle: Active fraction = 0.1; Idle fraction = 0.9. avgPower = 0.5 W×0.1 + 0.01 W×(0.9) = 0.05 + 0.009 = 0.059 W. 3. Raw life in hours: 6.66 Wh ÷ 0.059 W ≈ 112.88 h. Apply a 5 % safety margin: 112.88 × 0.95 = 107.24 h. 4. Convert to days for the secondary output: 107.24 ÷ 24 ≈ 4.47 days. Thus the calculator reports an estimated battery life of roughly 107 hours (≈4.5 days).

Inputs

  • Cell Capacity (mAh): 2000
  • Nominal Voltage (V): 3.7
  • Active Power Draw (W): 0.5
  • Idle Power Draw (W): 0.01
  • Duty Cycle (%): 10
  • Efficiency (%): 90
  • Safety Margin (%): 5

Result

  • Estimated Battery Life (h): 107.24
  • Estimated Battery Life (days): 4.47

Frequently asked questions

How do I estimate the duty cycle for my device?

Duty cycle is the proportion of time during each operating period that the microcontroller or sensors are actively powered. Measure or calculate the on‑time versus the total cycle length with a logger or code, then express it as a percentage.

Why is there an efficiency field and not only battery capacity?

Charge–discharge cycles are less than 100 % efficient; most Li‑Ion cells lose ~5‑10 % per round‑trip. The efficiency factor approximates these losses so the estimate reflects usable energy rather than raw capacity.

What if my device has multiple power states with different consumption levels?

Model the highest consumption as activePower, the lowest as idlePower, and set the duty cycle to reflect how often each level occurs. If you need finer granularity, add extra states manually or compute an equivalent weighted average to keep the calculator simple.

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