Battery Capacity (mAh) Enter the total battery capacity in milliampere-hours (e.g., 4000)

Average Current Draw (mA) Enter the average current consumed by the device in milliamperes (e.g., 250.5)

Quick Examples:

Smartphone Moderate Usage Wireless Sensor Low Power

Calculate Clear

This calculator is for informational purposes only. Verify results with appropriate professionals for important decisions.

Use this free online Battery Life Calculator to calculate your estimated battery runtime. Simply enter your battery capacity and average current draw to instantly get results in hours and minutes. This helps you plan power requirements for electronics projects, portable devices, and battery-powered applications.

How Estimated Battery Life Is Calculated

Battery life estimation uses a simple relationship between the total charge stored in a battery and the rate at which a device uses that charge. The battery capacity tells you how much electrical charge the battery can deliver, measured in milliampere-hours (mAh). The current draw tells you how fast the device uses that charge, measured in milliamperes (mA). By dividing the capacity by the current draw, you get the estimated operating time.

This formula works best for devices with steady, predictable power consumption. Real-world battery life may differ due to factors like temperature, battery age, and varying power demands.

What Your Battery Life Result Means

The battery life result shows the estimated time your device can run before the battery needs recharging. For example, a result of 10 hours means the battery should power the device for about 10 hours of continuous use. This estimate assumes the battery is fully charged and operates under ideal conditions.

Different devices have different typical runtime expectations. A smartphone might last 8 to 15 hours of active use, while a low-power sensor could run for weeks or months on a small battery. Here are some common reference points:

When planning a project, consider adding a safety margin of 20-30% to account for battery aging and real-world conditions.

Accuracy, Limitations & Common Mistakes of the Battery Life Calculator

How Accurate Is the Battery Life Calculator?

The calculator provides a good starting estimate for devices with steady power consumption. It works well for comparing different battery options or getting a rough idea of runtime. However, actual battery life can vary by 10-50% from the estimate depending on usage patterns, temperature, and battery health. For critical applications, testing the actual device with the intended battery is always recommended.

Limitations of the Battery Life Calculator

The calculator assumes a constant current draw, which rarely happens in real devices. It does not account for voltage changes as the battery discharges, which affects performance. The formula ignores efficiency losses in voltage regulators and other circuit components. Battery capacity also decreases with age, temperature extremes, and the number of charge cycles. Devices with varying power modes or sleep states will have different actual runtimes than the simple calculation suggests.

Common Mistakes to Avoid

• Using peak current instead of average: Many devices draw more current during peak activity. Use the average current over time for accurate estimates. Check device specifications or measure with a multimeter.
• Ignoring duty cycles: Devices that sleep most of the time use much less average current. A sensor that wakes for 1 second every minute has a very low average draw compared to its active current.
• Forgetting efficiency losses: Voltage regulators and other components waste some power. A 90% efficient regulator means you lose 10% of battery capacity as heat.
• Not accounting for battery cutoff: Batteries cannot be fully drained. Most devices stop working when voltage drops below a threshold, leaving unused capacity.

Frequently Asked Questions

Who is this Battery Life Calculator for?

This calculator is designed for electronics hobbyists, engineers, students, and anyone working with battery-powered devices. It helps with DIY electronics projects, product design, comparing battery options, and understanding how power consumption affects runtime.

How often should I use this calculator?

Use this calculator when planning new projects, comparing battery options, or estimating runtime for portable devices. For existing projects, you may want to recalculate when changing components or usage patterns that affect power consumption.

Does this calculator work for all battery types?

The calculator works for any battery type when you know the capacity in mAh and the current draw in mA. This includes lithium-ion, lithium-polymer, NiMH, NiCd, and alkaline batteries. Different battery chemistries have different discharge characteristics, so actual results may vary from the estimate.

Can I use this calculator for devices with variable power consumption?

Yes, but you need to calculate the average current draw first. For devices that sleep most of the time, multiply the sleep current by the sleep time and the active current by the active time, then average them. The calculator assumes a steady current draw over the entire runtime.

Is the Battery Life Calculator free to use?

Yes, this calculator is completely free to use. No sign-up is required, and it works on any device with a web browser.