Battery Life: 4:36
Cost Per Hour of Juice: $195 per hour
Here's a twist on the Windows 8 convertible you should probably avoid. The 12.5-inch ThinkPad Twist combines a swiveling touchscreen with one of the better keyboards you'll find. We especially like the stand mode for giving presentations. Just make sure you're near an outlet. On our battery test, the Twist died after 4 hours and 36 minutes. The average ultraportable notebook lasts 6:01. Although it has a slightly larger display, Lenovo's own IdeaPad Yoga lasted a much longer 6:18. In efficiency terms, the $899 Twist would cost you $195 per hour of juice, compared to $182 per hour for a $1,159 Yoga outfitted with a much faster 128GB SSD. That's an easy call in my book.