Buying a giant battery for the next blackout or off-grid adventure can be daunting, especially when hundreds or even thousands of dollars are on the line. Get it wrong and you’ve either spent too much money for something you’ll never use or discover that you didn’t buy enough ca pacity to keep your most important devices running. To get it right, you need to become intimate with the watt-hour (Wh). The watt-hour is a measure of capacity, or how much electrical energy a battery stores. If you know how much power — measured in watts — your devices consume, then the Wh rating of a battery lets you quickly calculate how long those devices will run. For example, a typical LED light bulb requires about 10W to illuminate. So a 1000Wh (1kWh) battery can run that bulb for 100 hours because Wh divided by watts gives you the time. For context, the average US home consumes about 889kWh per month, or about 29.2kWh per day, according to the US Energy Information Administration. During a blackout, you’d need about $15,000 worth of batteries on hand to keep it running for just one day (based on a rough average of 50 cents per Wh of battery capacity). But that’d be silly because you … Read the full story at The Verge. ...read more read less