Battery Life Calculator

About the Battery Life Calculator

Estimates how long a battery will last from its capacity (mAh) and the device's current draw (mA), with a derating factor for real-world efficiency.

How to use this calculator

1. Enter the battery capacity in \(mAh\).
2. Enter the device load in \(mA\).
3. Set the efficiency factor, if your calculator includes one, to account for real-world losses.
4. Read the estimated runtime in hours, then compare it with your expected use time.

The formula explained

The formula computes estimated runtime in hours by dividing battery capacity by current draw, then multiplying by efficiency. A larger capacity or higher efficiency increases runtime, while a larger load decreases it.

• capacity = battery capacity in \(mAh\), the amount of charge the battery can store
• load = device current draw in \(mA\), the amount of current the device uses
• efficiency = a decimal factor that adjusts for real-world losses, such as \(0.9\) for \(90\\%\) efficiency
• hours = estimated runtime in hours

Step by step method

1. Make sure capacity and load use the same current units, \(mAh\) and \(mA\).
2. Divide \(capacity\) by \(load\) to get the ideal runtime in hours.
3. Multiply by \(efficiency\) to adjust the estimate for real conditions.

Worked example

Problem. A battery has a capacity of \(3000\\,mAh\). A device draws \(250\\,mA\), and the efficiency is \(0.9\). Estimate the runtime.

1. Compute the ideal runtime, \(3000 \\div 250 = 12\).
2. Adjust for efficiency, \(12 \\times 0.9 = 10.8\).
3. The estimated runtime is \(10.8\) hours.

Tips and common mistakes

• Use the same units for capacity and load, because mixing \(mAh\) with \(A\) will give a wrong result unless you convert first.
• Remember that the estimate is not exact, because battery age, temperature, and device behavior can change the real runtime.

Frequently asked questions