Definition of "watt-hour" [watt-hour]

• A unit of energy, especially electrical energy, equal to the work done by one watt acting for one hour and equivalent to 3,600 joules. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "It supports Wi-Fi, Bluetooth and aGPS and includes a built-in 25-watt-hour lithium battery."
• "For comparison, the iPad 2 has a 25 watt-hour battery; the 11in MacBook Air model has a 35Wh battery, going up to 40Wh in the 13in model."
• "In the past 10 years alone, the energy density of lithium-ion batteries has doubled, and the price per watt-hour has fallen by more than 80%."