Battery Life Calculator

Created by Bogna Szyk
Reviewed by Małgorzata Koperska, MD and Steven Wooding
Last updated: Sep 12, 2022

Whether you're trying to figure out how long will a battery in your brand new laptop last or what will the runtime of your DIY electronic device be, look no further than this battery life calculator. It gives you a realistic approximation of the battery runtime based on its capacity and your device's energy consumption.

You can use this battery calculator in two ways. The default mode assumes that the battery runs continuously until it is discharged. If you open the advanced mode settings, you can analyze what happens if your device switches to sleep mode.

How to calculate the battery runtime?

It would be wonderful never to have to charge a smartphone again. You're probably painfully aware that no battery lasts forever, though. This battery life calculator finds out the approximate runtime of your battery based on the following formula:

Battery life = Capacity / Consumption × (1 - Discharge safety),


  • CapacityCapacity of your battery, measured in ampere-hours. You can usually find this value printed on your battery;

  • Consumption – Average current draw of your electronic device, expressed in amperes. (If you want to learn more about the electric current, make sure to check out the Ohm's law calculator!); and

  • Discharge safety – Percentage of your battery capacity that is never used. For example, if you use a LiPo battery to fly a drone, you should never discharge it below 20% – otherwise, it can be damaged. Our battery life calculator assumes a default discharge safety of 20%, but feel free to change it as you wish.

How long will a battery last: sleep mode

Now, let's imagine you are building an IoT device that spends most of the time in sleep mode. You'll probably want to calculate how long a battery will last in such a case. All you have to do is open the advanced mode to find out!

In the advanced mode, you can adjust the following additional parameters:

  • Awake time is simply the time that your device is not sleeping during one operational cycle – for example, 2 seconds.

  • Consumption in sleep mode is the average consumption of your device in sleep mode, measured in amperes. This value is probably much lower than the consumption in awake mode.

  • Sleep time is the time your device spends sleeping during one operation cycle.

💡 Here is an example of setting the awake and sleep times. If your device sleeps for 80% of the time, set the sleep time to 8 seconds and the awake time to 2 seconds.

Based on the parameters listed above, the battery life calculator finds the average consumption according to the equation:

Average consumption = (Consumption1 × Time1 + Consumption2 × Time2) / (Time1 + Time2),

where index 1 describes the awake mode, and index 2 is the sleep mode.

After determining the average consumption, our calculator substitutes the regular battery life formula to figure out the runtime of your battery.

Bogna Szyk
Battery capacity
Discharge safety
Device consumption
Battery life
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