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Battery Life Calculator

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How to calculate the battery runtime?How long will a battery last: sleep modeFAQs

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),


  • Capacity – Capacity of your battery, measured in ampere-hours – you can usually find this value printed on your battery (or use our battery capacity calculator);

  • 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.

💡 If you fly drones, then you might find our drone flight time calculator useful.

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 related information and runtime section to find out!

In the related information and runtime section, 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 – which our battery size calculator can do.


What does battery life mean?

Battery life is the total amount of time a device can be operated before needing to be recharged. Battery lifespan, on the other hand, stands for the number of times your battery can be recharged before it dies and needs to be replaced. How you use your device will be one of the critical determinants of how long your device's battery life and battery lifespan will be.

How do I calculate the life of a battery?

To calculate the battery life of a device, you need to:

  1. Find out what your device's battery capacity is. Usually, this value is printed on the battery.

  2. Determine what the discharge safety of your device is. If unknown, you can assume a discharge safety of 20%.

  3. Establish the average consumption of your device (average current draw).

  4. Substitute these values in the battery life formula as follows:

    battery life = battery capacity / device consumption × (1 - discharge safety)

That's it! Now you know how to calculate your battery's runtime!

How do I find the average amp draw of a device?

To find the average current draw of a device, you can:

  1. Check whether a wattage specification is indicated on the bottom or back of the device.

    If you cannot find this, search online for an average wattage value corresponding to your device type.

  2. Find out what the power source's voltage is.

    The power source can either be an outlet or a battery.

  3. Divide the wattage (in watts) by the voltage of the power source (in volts) as follows:

    average current draw = wattage rating / power source

How long does a 4500 mAh battery last?

A device with a battery capacity of 4500 mAh would last 6 hours. This is assuming that:

  • The discharge safety is 20%;
  • The average consumption is 1 A.

These are the usual values for a typical smartphone. For more precise values, please consider:

  • The type of device you are dealing with;
  • How often you use the device;
  • The activities you engage in (ex. listening to music, downloading files, making calls, etc.).


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