Battery Life Calculator Formula

Understand the math behind the battery life calculator. Each variable explained with a worked example.

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Formulas Used

Battery Life

life_hours = capacity_mah * eff_fraction / load_current_ma

Battery Life (days)

life_days = capacity_mah * eff_fraction / load_current_ma / 24

Usable Energy (at 3.7 V)

energy_wh = capacity_mah * eff_fraction * 3.7 / 1000

Variables

VariableDescriptionDefault
capacity_mahBattery Capacity(mAh)2000
load_current_maLoad Current(mA)150
efficiency_pctDischarge Efficiency(%)85
eff_fractionDerived value= efficiency_pct / 100calculated

How It Works

Battery Life Estimation

Formula

Life (hours) = Capacity (mAh) x Efficiency / Load (mA)

Efficiency accounts for losses from the battery internal resistance, DC-DC conversion, and temperature effects. Typical Li-ion efficiency is 80-90%.

Worked Example

2000 mAh battery, 150 mA load, 85% efficiency.

capacity_mah = 2000load_current_ma = 150efficiency_pct = 85
  1. 01Usable capacity = 2000 x 0.85 = 1700 mAh
  2. 02Life = 1700 / 150 = 11.3 hours
  3. 03Life in days = 11.3 / 24 = 0.47 days

Ready to run the numbers?

Open Battery Life Calculator