What is an Amp Hour?

Whenever you are battery shopping for either your car, UPS, or anything else, you will encounter several terms used to define the batteries, including amp hour. In order to be able to buy the right type of battery, you need to be familiar with what an amp hour is.

An amp-hour basically defines how long a battery takes to provide a power of exactly one ampere in one hour. However, since most commonly used batteries don’t draw precisely one amp of current, this definition is based more on understanding than application.

Fret not, as our guide below details everything you need to know about an amp hour and its inseparable relation with an amp hour rating.

So, let’s get started!

What is an Amp Hour Rating?

What is an Amp Hour?

Amp-hour rating refers to the amperage a battery can deliver for precisely one hour. The batter’s amp-hour along with its discharging time constitutes the amp hour rating. It helps you in judging a battery’s life and comparing it with other similar batteries.

Normally, you’ll find the amp hour rating visibly displayed on your battery or on the relevant sales information. If that’s not the case, then you are dealing with a starting battery that is not designed to deliver consistent power in amp-hours.

Amp Hour Rating and Battery Capacity

Generally speaking, an amp hour rating does give you a bit of an insight into a battery’s capacity. For example, under similar conditions, a 20 Ah battery will last twice as long as compared to a 10 Ah battery. Also, the former will require fewer recharging halts as compared to the latter.

However, the exact number of hours both of these batteries will last can’t be determined merely based on their advertised amp hour rating. For that, many other factors, such as the battery’s age, the number of charging and discharging cycles, temperature, and its voltage ratings, also go into play.

Once these factors are determined, you will have to put your battery to the test.

Representations of Amp Hour Rating

What is an Amp Hour?

Amp-hour rating is mentioned in different sub-units of power in different types of batteries.

In small, low-powered batteries, it is usually represented in mill-amp hours (mAh) whereas, on large batteries, the unit amp-hour (Ah) is used.

Furthermore, there is another form of rating representation that most deep cycle batteries use, namely C rating. It’ll tell you the exact number of amp-hours a battery can provide for the specified time.

For instance, a C rating of C-10 may mean that your battery provides you 30 amp-hours of power in 10 hours without dropping off. Similarly, the same battery with a rating of C-50 can provide you safely with 35 amp-hours of power in 50 hours.

Depending upon your requirement, compare the C ratings of a battery with its corresponding amp-hour ratings, and you should get a good enough idea of which C rating works for you.

Do Greater C-ratings Means Greater Power?

A rechargeable battery provides greater power when it runs for longer. How is that so?

So, basically, what happens is that when you rapidly discharge a battery with, for instance, a C-10 rating, you are causing the battery to lose some of its power in the form of heat.

Meanwhile, a battery with a C-100 rating doesn’t produce as much heat since it runs gradually, making it more efficient.

Calculating Amp Hour and Amp Hour Rating

If you can determine the current in your battery in a given time, you can use the following equation and compute the amp hours:

Amp Hour (Ah) = Current (I) x Discharge Time (T)

Employing basic mathematical knowledge, just put in the known values in the equation above, and you should be able to find the Amp-hours of your battery.

The combination of the obtained value and the time for which the battery is run is called the amp hour rating.

Frequently Asked Questions

What is an Amp Hour?

How Long Will a 100 Ah Battery Run an Appliance that Requires 1000 W?

Approximately 0.52 hours or 31 minutes.

Does a Higher Ah Battery Give More Power?

Yes, especially in the case of heavy-duty tasks.


We genuinely hope you’ve got everything you were looking for regarding an amp hour out of this guide.

Since amp-hour somewhat determines the battery’s capacity, having a firm understanding of the term will go a long way in helping you to find suitable batteries for your needs.

Liam Weissman

Hello and welcome to PowerToolGenius! My name is Liam and for the last 9 years, I have worked extensively with various power tools and accessories. I have tested hundreds of different brands and models and understand the industry extensively and have been working with tools my entire life!

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