What Is a Battery Life Calculator?

A Battery Life Calculator helps you estimate how long a battery will power your device based on its capacity, the device's current draw, and circuit efficiency. Whether you're building an Arduino project, designing an IoT sensor node, or simply curious about how long your power bank will last, this tool provides quick and accurate estimates.

Battery Life Mode

Enter your battery capacity and current draw to find out how long it will last

Required Capacity Mode

Enter your desired runtime and current draw to find out what battery capacity you need

Why Efficiency Matters: Real-world circuits don't deliver 100% of the battery's stored energy to the load. Voltage regulators, DC-DC converters, and other components introduce losses. The efficiency slider (default 85%) accounts for these losses, giving you a more realistic estimate than a simple mAh ÷ mA calculation.

How to Use the Calculator

Calculate How Long Your Battery Will Last

Select Mode

Choose the Battery Life tab (default mode)

Enter Battery Specs

Input your battery's capacity in mAh or Wh, and its voltage

Set Current Draw

Enter the current draw of your device in mA

Adjust Duty Cycle

Set the duty cycle if your device isn't always active (e.g., 10% for a sensor that wakes every 10 minutes)

Configure Efficiency

Set the efficiency slider to match your circuit (typically 80–90% for regulated circuits)

View Results

The result updates in real time as you type

Determine What Battery Capacity You Need

Switch Mode

Select the Required Capacity tab

Set Desired Runtime

Enter your desired runtime in hours

Configure Parameters

Enter the current draw and adjust efficiency and duty cycle settings

Get Capacity Requirements

The calculator shows the minimum battery capacity (mAh and Wh) needed

Using Battery Presets

Click Presets to see a grid of common battery types. Clicking a preset automatically fills in the capacity and voltage fields. Available presets include CR2032, AAA, AA, 9V, 18650, LiPo (1S/2S/3S), lead-acid, and power bank batteries.

Multiple Loads

Click Add Load to add additional devices sharing the same battery. Each load can have its own name, current draw, and duty cycle. The calculator combines all loads to compute the average total current, and shows a breakdown chart of each load's contribution.

Key Features

Dual Calculation Modes

Switch between Battery Life (how long will it last?) and Required Capacity (what battery do I need?) with a single click.

Instant mode switching
Both modes support multiple loads
Efficiency adjustment in both modes

Multiple Load Support

Real projects often have multiple components drawing power simultaneously. Add as many loads as needed.

Individual current and duty cycle per load
Visual load breakdown chart
Automatic total current calculation

Battery Presets

Quickly select from 12 common battery types with pre-configured capacity and voltage values.

Coin cells (CR2032)
Alkaline (AA, AAA, 9V)
Lithium-ion (18650)
LiPo (1S/2S/3S)
Lead-acid (6V, 12V)
Power banks

Duty Cycle & Efficiency

Model intermittent operation and real-world circuit losses for accurate estimates.

Duty cycle for sleep modes
Efficiency slider (default 85%)
Realistic power consumption modeling

Visual Feedback

Intuitive visual indicators help you understand your battery performance at a glance.

Color-coded battery bar (green/yellow/red)
Load breakdown chart
Formula display with values

Quick Examples

Four pre-configured examples demonstrate real-world scenarios to get you started quickly.

Arduino with sensor
ESP32 in deep sleep mode
LED strip on 12V battery
Phone charging from power bank

Frequently Asked Questions

What is the difference between mAh and Wh?

mAh (milliamp-hours) measures charge capacity at a specific voltage. Wh (watt-hours) measures total energy regardless of voltage.

Conversion formula: Wh = mAh × V ÷ 1000

Use mAh when comparing batteries of the same voltage
Use Wh when comparing batteries of different voltages

What efficiency value should I use?

It depends on your circuit type. Different voltage regulators and converters have varying efficiency levels:

Linear Regulator

50–70% efficient (e.g., LM7805)

Switching Regulator

80–95% efficient (buck/boost converter)

Direct Connection

95–100% efficient (no regulator)

What is duty cycle?

Duty cycle is the percentage of time a load is actively drawing current. This feature is essential for modeling devices with sleep modes or intermittent operation.

Example: An IoT sensor that wakes for 1 second every 100 seconds has a 1% duty cycle. This dramatically extends battery life compared to continuous operation.

Continuous Operation

100% Duty Cycle

Device always active
Maximum power consumption
Shortest battery life

Sleep Mode

1% Duty Cycle

Device sleeps 99% of time
Minimal average power draw
100× longer battery life

Why is my actual battery life shorter than calculated?

Several factors can reduce real-world battery life beyond the theoretical calculations:

Temperature

Cold weather significantly reduces battery capacity and performance

Self-discharge

Batteries slowly lose charge even when not in use

Voltage Cutoff

Devices stop working before the battery is fully depleted

Current Spikes

Peak currents (e.g., WiFi transmission) may exceed average measurements

Battery Age

Older batteries have reduced capacity and higher internal resistance

Best practice: Add a 20-30% safety margin to your calculations to account for these real-world factors.

How do I measure my device's current draw?

Accurate current measurement is essential for reliable battery life estimates. Here are the recommended methods:

Choose Measurement Tool

Use a multimeter in series with the power supply, or a USB power meter for USB-powered devices

Measure Different States

For devices with variable draw (like microcontrollers with sleep modes), measure both active and sleep currents separately

Use Duty Cycle Feature

Combine multiple measurements using the duty cycle feature to get accurate average current draw

Pro tip: For microcontrollers, use a low-side current sense amplifier or specialized tools like the Nordic Power Profiler Kit for accurate sleep current measurements (often in the µA range).