What is an Amp Hour?

Batteries, we all have plenty of devices in our homes that contain a variety of battery types. Often individuals are just looking to replace AA, AAA, or some other very common type and not much thought is required. However, if you have ever been looking to upgrade a battery, you’ve likely noticed a term called “amp hour”.

So, what does that mean, and how can it help you with the decision process? All batteries have a maximum amount of energy that they can disperse, as laid out by the manufacturer, under “normal circumstances”.

Amp hour is the measurement of this energy in reference to time. Let’s assume a device requires 1 A of steady current draw. If a battery used to power the device has an amp hour rating of 1 Ah, the device would be powered for approximately 1 hour. Easy math, right?

Now, most applications won’t have math that easy. To help with that DigiKey has a Battery Life Calculator so you can easily type the numbers in and see the results. To test it, let’s go over another scenario. If the device has a steady current draw of 60 mA, and the battery used to power it is rated for 480 mAh, the device should be powered for approximately 8 hours (480/60=8).

As mentioned earlier, these are based on normal or ideal circumstances. Things that could affect the life of the battery include, but are not limited to:

• Ambient Temperature
• Current Peaks
• Battery Chemistry
• Cycling of the Device
• Application

Therefore, the Battery Life calculator should be used for estimates only and not relied upon as a truly accurate battery life indicator.