What Are Amp Hours? + How to Calculate Battery Capacity

What Are Amp Hours?

Amp hours (or ampere hours), often referred to simply as “Ah”, are a unit of measurement that gauges a battery’s capacity.

More technically, it takes into account both the amount of time a battery requires to fully discharge and the amount of current during that time.

Important: Don’t mistake amp hours for how many hours your battery will last. We’ll dive into the details more later in the “how to calculate amp hours” section.

For now, however, know that amp hours refers to how many amps you have available to use. How long your battery lasts will then be a measure of how many amps you’re pulling per hour. 

What Is the Difference Between Amps and Volts?

Now that you know what amps are, how do they differ from volts?

Electricity is measured using three different units:

• Amps
• Volts
• And ohms

While amps measure a battery’s capacity, volts are a measure of voltage, the actual force that drives electricity and pushes electrons through electrical wires.

Ohms measures resistance, and it essentially has to do with the efficiency of the electrical production itself, minimizing heat to maximize amps and volts.

How to Calculate Your Battery’s Capacity (Using Amp Hours)

To calculate your battery’s capacity, i.e. your amp hours, and figure out how long your battery will last, you just need to know your battery’s amp hours.

The equation for figuring out amp hours is:

• Amp hours (Ah)  = Current x Discharge Time

Current is how many amps you’re pulling, while discharge time is how long you’re pulling those amps (i.e. are you drawing from your battery for an hour, two hours etc.).

With that said, you don’t need to calculate amp hours yourself. Most modern batteries list their amp hours clearly on the battery itself.

Don’t be confused, though. The “hours” in “amp hours” does not refer to the amount of time the battery will last.

Instead of thinking of the number of amp hours as the amount of time (hours) your battery will last, think of it simply as a measure of the energy you have available. 

Knowing how many amps you’re using per hour will allow you to calculate how long your battery will last. 

For example, 10Ah or 10 amp hours will last 10 hours if you’re pulling 1 amp of current per hour from the battery.

However, what if you’re pulling more than that from your battery?

If you’re pulling 2 amps of power, it will only last for 5 hours (2 amps per hour x5 = 10 amps).

And if you’re pulling 10 amps? The battery will last one hour. 

The average RV battery has around 80 amp hours of power. So, if you’re drawing 5 amps per hour then your battery will last about 16 hours. 

How Long Can a 100-Amp Hour Battery Last?

The average number of amps used per hour on an RV battery are 5-10, which would mean a 100-amp hour battery will last 10-20 hours. 

Keep in mind that you may be drawing more or less amps from your own battery, however.

You’ll need to know exactly how many apps you’re pulling from your battery to know how long it will last.

The most commonly suggested way to do that is with a multi-meter, like this one from AstroAI:

But some also suggest a clamp meter for easier access to hard-to-reach spots and a bit more utility:

Are AC Power and DC Power the Same?

Direct current or “DC” power is the type of power that is stored in your average RV battery.

Alternative current or “AC” power is the type used to power all your standard appliances like refrigerators, AC, microwaves, and electronic devices.

If you’re shopping for an RV battery, you’ll see DC power mentioned. You can get by with that for most average use, but you’ll be limited in what you can power and run the risk of damaging more sensitive devices such as smartphones and laptops.

To avoid this, you can get an inverter generator that allows you to convert the DC power in your battery to AC power. 

Learn more about the pros and cons of inverter generators here: dustytrailrv.com/pros-cons-inverter-generators

And check out our top picks for the best inverter generators: