Electronics Tools / Calculator

Battery Life Calculator

Estimate how long a battery can power a constant or duty-cycled load using capacity, energy, current, voltage, and realistic system assumptions.

Live energy-flow estimate

Battery to load

Two amp-hour battery powering a 100 milliamp load for an estimated 20 hours A technical energy-flow diagram showing a fully usable battery module connected to a constant-current device load. 100 mA average EFFECTIVE BATTERY2000 mAhESTIMATED RUNTIME20 hours

Estimated battery life

20 hoursIdeal constant-current estimate

Actual runtime can be lower because of battery condition, temperature, cutoff voltage, discharge rate, and device behavior.

Nominal source
2000 mAh
Usable amount
2000 mAh
Average load
100 mA
System efficiency
Not applied

Calculation breakdown

How this estimate was calculated

Effective capacity

2000 mAh × 100% = 2000 mAh

Estimated runtime

2000 mAh ÷ 100 mA = 20 hours

Formula reference

Battery runtime relationships

Capacity and current

Runtime (h) = Capacity (Ah) ÷ Battery current (A)

Energy and power

Runtime (h) = Energy (Wh) ÷ Load power (W)

Capacity to energy

Energy (Wh) = Capacity (Ah) × Battery voltage (V)

Active and sleep load

Average current = Σ(Current × time share)

This is an idealized estimate, not a guaranteed runtime. Chemistry, temperature, age, discharge rate, voltage cutoff, conversion losses, and changing device behavior can reduce actual battery life.

Practical examples

Common estimates

2000 mAh · 100 mA20 hours ideal
5000 mAh · 250 mA · 80% usable16 hours ideal
100 mA active · 1 mA sleep · 10% active10.9 mA average

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