Does this include efficiency losses?

No. Real systems lose some energy through regulators or heat. Add a buffer for conversion losses.

Can I enter watts instead?

Convert watts to milliamps using mA = (Watts ÷ Volts) × 1000, then plug into the calculator.

How do duty cycles affect runtime?

If your device sleeps part of the time, use an average mA draw across active + sleep periods for a better estimate.

Does battery aging change the result?

Yes. Capacity declines over cycles and in cold temps. Derate capacity to be conservative.

What voltage should I enter for a pack of cells?

Use the nominal voltage of the pack configuration (e.g., 7.4 V for 2S Li-ion). It’s for Wh calculation only; runtime is mAh ÷ mA.

tech calculator

Battery Life Calculator

Estimate runtime from battery capacity, average load, and voltage.

Results

Runtime (hours): 6.25
Runtime (days): 0.26
Battery capacity (Wh): 18.50
Percent consumed per hour: 16.00%

How to use this calculator

Enter battery capacity in mAh.
Enter device draw in mA (average current).
Optionally set voltage to see watt-hours.
Review runtime in hours/days and percent per hour.

Inputs explained

Battery capacity (mAh): Rated battery capacity in milliamp-hours.
Device draw (mA): Average current consumption. Use an ammeter or device spec sheet.
Battery voltage (V): Nominal voltage to convert mAh to Wh (3.6–3.8 V typical for Li-ion cells).

How it works

Runtime hours = battery capacity (mAh) ÷ device draw (mA). We also convert mAh to watt-hours using voltage.

Percent per hour shows how fast the battery would drain when the device runs continuously at that draw.

Formula

Runtime (h) = Capacity ÷ Draw
Wh = (mAh ÷ 1000) × Voltage

When to use it

Estimating IoT sensor runtime on a battery pack.
Checking if a UPS or power bank can bridge outages for routers or modems.
Planning field gear battery swaps for shoots or events.

Tips & cautions

Actual draw fluctuates—use an average that includes active and idle modes for realistic results.
Regulator inefficiencies and DC-DC converters reduce real runtime; add buffer (10–20%) for losses.
Colder temps and battery age also reduce capacity; plan conservatively for critical gear.
Assumes constant draw and nominal voltage; doesn’t model duty cycles or surge currents.
Battery capacity degrades over time and with temperature.
Regulator efficiency and cutoff voltages can materially change runtime.

Worked examples

5,000 mAh pack powering 800 mA router

Runtime ≈ 6.25 hours
Battery ≈ 18.5 Wh

10,000 mAh pack powering 300 mA sensor

Runtime ≈ 33.3 hours (≈1.4 days)

Deep dive

This battery life calculator converts capacity and current draw into runtime. Enter mAh, average mA draw, and voltage to see hours, days, watt-hours, and percent consumed per hour.

Use it to plan power banks, IoT nodes, or UPS backups. Add buffer for regulator losses, cold weather, and aging cells to avoid surprises in the field.

FAQs

Does this include efficiency losses?: No. Real systems lose some energy through regulators or heat. Add a buffer for conversion losses.
Can I enter watts instead?: Convert watts to milliamps using mA = (Watts ÷ Volts) × 1000, then plug into the calculator.
How do duty cycles affect runtime?: If your device sleeps part of the time, use an average mA draw across active + sleep periods for a better estimate.
Does battery aging change the result?: Yes. Capacity declines over cycles and in cold temps. Derate capacity to be conservative.
What voltage should I enter for a pack of cells?: Use the nominal voltage of the pack configuration (e.g., 7.4 V for 2S Li-ion). It’s for Wh calculation only; runtime is mAh ÷ mA.

Related calculators

tech

Data Transfer Rate Converter

Convert Mbps, MB/s, and KB/s values to compare network and storage speeds.

Runtime assumes a constant draw and nominal voltage. Temperature, battery age, and regulator efficiency affect real-world results.