Battery Life Calculator

Estimate battery life, required battery capacity, or average current from duty cycle for portable electronics, embedded devices, sensors, LED systems, and battery-powered prototypes.

The result is a first-pass engineering estimate based on nominal capacity, average current, and usable battery efficiency. Real products still need validation against battery chemistry, temperature, aging, discharge rate, and cutoff voltage.

Engineering tool

Battery Life Calculator

Estimate battery life, required battery capacity, or average current from duty cycle with engineering-unit conversion.

Calculator mode

Battery capacity

Nominal or usable battery capacity.

Load current

Average current drawn by the circuit.

Battery efficiency

Usable capacity or conversion efficiency from 1% to 100%.

Battery Life

20 h

Estimate assumes constant average current and usable battery capacity.

Result console

Battery life: 20h
Battery life: 1,200min
Battery life: 20h
Battery life: 0.833333days
Battery capacity: 3Ah
Load current: 150mA
Battery efficiency: 100%
Formula used: t = Capacity × η / I

This result assumes constant average current and nominal battery capacity. Real runtime depends on chemistry, temperature, aging, cutoff voltage, discharge rate, and load profile.

Formula reference

Battery Life Formulas

Use amp-hours, amperes, hours, efficiency as a 0 to 1 factor, and duty cycle as a 0 to 1 factor internally.

t = Capacity × η / ICapacity = I × t / ηIavg = Iactive × D + Istandby × (1 − D)

Variable definitions

Capacity: Battery capacity in Ah or mAh
I: Average load current in A or mA
Iavg: Average current from active and standby states
Iactive: Current during active operation
Istandby: Current during sleep, idle, or standby operation
t: Battery life or runtime in hours
η: Battery efficiency or usable capacity factor
D: Duty cycle as a fraction from 0 to 1

Variable Description

Capacity: Available battery charge, commonly entered in mAh or Ah.
Current: Load current drawn by the circuit, usually measured as average current.
Average Current: Equivalent constant current calculated from active and standby operating states.
Runtime: Target operating time or calculated battery life.
Efficiency: Usable capacity factor that accounts for conversion loss, cutoff reserve, and practical derating.
Duty Cycle: Percentage of time spent in active operation.
Battery Life: Ideal operating time before usable capacity is consumed.

Worked Examples

Battery Life

Capacity = 3000 mAh, load = 150 mA, efficiency = 100%

Battery life = 20 hours

Battery Life with Efficiency

Capacity = 2 Ah, load = 500 mA, efficiency = 90%

Battery life = 3.6 hours

Required Capacity

Runtime = 24 hours, average current = 120 mA, efficiency = 90%

Capacity ≈ 3.2 Ah

Average Current from Duty Cycle

Active = 200 mA, standby = 5 mA, duty = 20%

Average current ≈ 44 mA

Battery Capacity

Nominal capacity is usually specified at a defined discharge current, temperature, and cutoff voltage.

Average Current

Average current is often more useful than peak current for estimating battery life in duty-cycled electronics.

Duty Cycle

Duty cycle can dramatically reduce average current when active time is short and standby current is low.

Battery Runtime Estimation

Runtime estimates are most accurate when the load profile and usable capacity are measured.

Battery Efficiency

Efficiency can represent converter loss, capacity reserve, or usable discharge depth.

Constant Current Assumption

This calculator assumes the average current remains constant over the discharge period.

Battery Aging

Rechargeable batteries lose capacity with cycle count, calendar age, and operating temperature.

Temperature Effects

Cold temperatures reduce available capacity, while hot operation accelerates degradation.

Battery Chemistry Differences

Lithium-ion, NiMH, and lead-acid batteries have different discharge curves and usable capacity behavior.

Cutoff Voltage

Many systems stop operating before the battery is fully discharged because regulators or protection circuits need minimum voltage.