One reader has an interesting question over at Slate: Which option uses less electricity, plugging in a laptop or using the battery? The short answer, plugging it in while in use is more efficient. Energy is lost in the process of the charging and storing electricity in the battery. Kudos to those of you who know enough about electricity to figure this out on your own.
But there are a couple of caveats to that short answer. Most laptops are set to run at a higher power setting when plugged in. Users should change their power settings to make sure their laptops run at the same power level regardless of whether they are plugged in or running off battery power. Also, make sure laptops are only plugged in when they are being used. Plugged in computers are draining small amounts of power even when they are powered off (called "vampire power"). Homeowners can read more about managing their power consumption in this article.
This "vampire power" also applies to certain appliances such as toasters, blenders, and such. They seem so harmless to leave plug in between usage, but they are slowly draining power and using electricity.