How to Calculate 12 Volt Amp-Hours

Save

Amp-hour ratings are how manufacturers rate a battery's electrical capacity, in the same way you might rate a bucket's water capacity in gallons. Manufacturer amp-hour ratings are helpful when comparing different batteries and different brands, but be forewarned: all isn't necessarily what it appears to be on the label.

What is an Amp-Hour?

  • An amp-hour -- properly "ampere-hour" -- is a unit of measure describing electrical charge capacity. If a battery is said to have "20 amp-hours of capacity," it means that it can hypothetically discharge one amp of current for 20 hours, 20 amps for one hour, or any combination of amps and hours that equal 20 amp-hours. That might be five amps for four hours, 10 amps for two hours, or 6.66 amps for three hours.

Run-Time for Accessories

  • In theory, you can calculate the run-time for any of your battery's accessories by dividing the amp-hour rating of the battery by the amp draw of the accessory. You might have to convert from watts first. For instance, if you want to know how long you can bang a 1,000-watt stereo system on a heavy-duty 100-amp-hour battery, start by dividing the wattage by the voltage -- 12 volts, in this case -- to arrive at an 83.3-amp draw for the stereo system. Divide the battery's 100-amp-hour capacity by 83.3, and you get 1.2 hours, or about 1 hour and 12 minutes of tunes before the battery dies.

Caveat

  • Manufacturers test and rate batteries according to a certain discharge time -- in the automotive industry, usually 20 hours. In theory, that doesn't affect the actual amp-hour rating, but it does make a difference on how long your battery will last if you consistently discharge it outside of that 20-hour parameter. If you're using a standard battery rated for a 20-hour discharge, and you routinely kill it in an hour with a banging stereo, or 150 hours with a tiny trunk-light bulb that won't shut off, then the battery won't be long for this world.

Promoted By Zergnet

Comments

You May Also Like

  • 12 Volt Vs. 6 Volt Batteries

    Considered low-voltage batteries, 12-volt and 6-volt batteries are similar in basic construction; they are both categorized as lead-acid batteries. However, they differ...

  • How to Calculate Kilowatt Hours

    A kilowatt-hour is a basic unit of energy that applies especially to electricity. A watt is a volt times an amp, and...

  • How to Calculate Battery Watt-Hours

    If you're a recreational vehicle owner, knowing how long your battery will provide power is important. And that's because your battery will...

  • How to Calculate AH for a Battery

    Based on an appliance's wattage and the voltage of the attached battery, the appliance will draw a specific amount of current through...

  • How to Calculate Battery Amperage Life

    Battery amperage life, the number of ampere-hours that a battery can supply, is dependent on a number of factors. One of the...

  • How to Determine the AH of a 12-Volt Battery

    Batteries are rated according to the tasks they are expected to perform. Batteries rated with cranking amps are designed to deliver high...

  • Watt Hour Vs. Amp Hour

    Electricity carries energy that you can measure in several different ways. Power, the rate at which equipment uses energy, is expressed as...

Related Searches

Check It Out

How To Travel For Free With Reward Points

M
Is DIY in your DNA? Become part of our maker community.
Submit Your Work!