Converting amp hours to kilowatt hours is often necessary if you want to compare the amount of power you can obtain from different energy generation devices, such as wind, hydro power and solar energy generators, and energy storage devices, such as batteries. It's a simple process to convert amp hours to kilowatt hours; a few arithmetic operations and you're done.
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Obtain the amphour rating of your energy generation or energy storage device. A boat battery, for example, may list a 0.8 amphour rating. This rating could be listed on the side of the product, or in the owner's manual. Instead of amp hours, the rating also could be listed in milliampere hours, often abbreviated mAHr.
To convert milliampere hours to amp hours, divide the milliamperehour rating by 1,000. For example, If a battery is rated at 3,500 milliampere hours, the amphour rating would be 3.5 amp hours, since 3,500 divided by 1,000 is 3.5.

Determine the operating voltage of your energy generation or energy storage device. Batteries are also given a voltage rating, often listed right on the side. Common voltage ratings for batteries include 3.3 volts, 5 volts and 12 volts. To determine exactly the voltage level of your battery, the best approach is to measure the voltage across the battery. The battery, if not fully charged, could have a lower voltage level than what is indicated on the battery.

Calculate the watthour rating. Multiply the amphour rating by the voltage rating. If you have a battery that has a 0.8 amphour rating, and the battery has a voltage rating of 12 volts, the watthour rating would be 9.6 watt hours, since 12 times 0.8 is 9.6.
In other words, the battery could power a device that requires 9.6 watts for one hour. Likewise, if you had a battery with a 0.8 amphour rating, it could power a 0.8amp device for one hour.
Watts formula, a formula to compute power, states that the power in satts is equal to the current multiplied by the voltage. If a device requires 3 amps of curent and the battery that it uses is a 30volt battery, the power the device uses is 90 watts, since 3 times 30 is 90.
The formula for watt hours is an extension of watts formula. It states that watt hours is equal to amphours multiplied by the voltage across the device.

Calculate the kilowatthour rating. One kilowatt hour equals one thousand watt hours. Convert watt hours to kilowatt hours by dividing the watthour rating by 1,000. For a 9.6 watthour rating, the kilowatthour rating would be 0.0096 kilowatt hours, since 9.6 divided by 1,000 is 0.0096.
Tips & Warnings
 Very powerful and dangerous batteries will often be rated in kiloamperes. A kiloampere is equivalent to 1,000 amperes (amps). To convert kiloampere hours to amp hours, multiply the kiloamperehour rating by 1,000. For example, if battery is rated at 3 kiloamp, it will have an amphour rating of 3,000 amp hours, since 3 multiplied by a 1,000 is 3,000.
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