How To Calculate Watt-Hours Of A Battery? Easy 2-Step Math

Alright, watt-hours of a battery. This is the best metric for battery capacity, not the amp-hours (like 100Ah, 200Ah battery, for example). Let’s learn how to calculate the watt hours of a battery step-by-step. No panic here; it’s an easy 2-step thing, and we’ll show you how.

Quick example of why knowing watt-hours (Wh) is useful: A 100Ah 12V lithium battery has a 1,200 Wh capacity. That means that it can run:

  • A 1,200 watt appliance for 1 hour.
  • A 1 watt appliance for 1,200 hours.
  • A 100 watt appliance for 12 hours, and so on. You get the point.
how to calculate watt hours of a lithium battery
Inner structure of a 100Ah lithium battery.

Now, to calculate battery watt hours, we will need only 2 key metrics:

  1. Amp hours (Ah). This is your 100Ah battery, for example.
  2. Voltage (V). Most batteries have a 12V voltage. Some bigger batteries can have 24V or even 48V voltage.

Fortunately, all batteries will have both Ah capacity and voltage prescribed on the battery itself (or the label). Obviously, these battery labels lack the capacity in watt-hours; that’s why we need to calculate Wh ourselves.

Here’s how we can do just that:

Calculating Wh Of A Battery (Step-By-Step)

  1. Check the battery and find the Ah capacity and voltage (V) on the battery. Example: 100Ah battery with 12V voltage.
  2. To calculate watt hours, just multiply the amp hours by voltage. Here’s the equation:
    Wh = Ah × V

That’s it.

To demonstrate how easy it is, we can use that 100Ah battery as an example. So, we have a 100Ah battery, and it produces 12V voltage. How many Wh is a 100Ah battery? Let’s put both of these figures in the equation:

Wh (100Ah, 12V Battery) = 100Ah × 12V = 1,200 Wh

There you have it:

We have successfully calculated that a 100Ah 12V battery has a 1,200 Wh capacity. That’s the same as 1.2 kWh (in kilowatt-hours).

You can use this 2-step process to calculate watt hours of a battery bank as well.

Example: Let’s say you have a 20,000 mAh (20Ah) 6V battery bank. How many watt hours capacity does such a battery bank have? Let’s put both numbers in the watt hours equation like this:

Wh (20Ah, 6V Battery Bank) = 20Ah × 6V = 120 Wh

20,000 mAh battery bank, running on 6V voltage, has a 120 Wh capacity.

how to calculate watt hours of a battery bank
This is a 20,000 mAh 6V battery bank. It has a 120 Wh capacity, as calculated above.

We hope that this illustrates well how to calculate watt hours for any battery. If you need a bit of help, you can always use the comment section below, give us some numbers, and we will help you out.

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