Android tablets, large or small, can’t seem to match the battery life of the iPad. In a recent set of battery life tests, Apple’s new iPad has the longest battery life among 10-inch tablets; in the 7-inch category, the iPad Mini comes out on top as well.

UK consumer watchdog site Which? tested the battery life of tablets for Web browsing over Wi-Fi (or 3G if available) and video playback. The brightness was set to around 200 nits using a light meter on all tablets so no manufacturer can get an advantage due to some default low brightness settings.

Which? Battery tests for 10-inch tablets (click to enlarge)

In the large tablets category, the iPad with Retina display led test results with 811 minutes (13.5 hours) of battery life, with the iPad 2 in the second spot at 590 minutes (9.8 hours). The highest performing Android tablet in this category was the Sony Xperia Tablet S at 534 minutes, closely followed by the Samsung Galaxy Tab 2 10.1.

Microsoft’s Surface RT tablet was included in the large tablet battery life tests, and scored a respectable 501 minutes (8.3 hours). Near the bottom of the rankings was the new Google Nexus 10, with a Retina-beating high-res display, but with only 488 minutes (8.1 hours) of battery life. The Asus Eee Pad Transformer Prime was the last in the scores, with 335 minutes of battery life without its separate keyboard, which can extend the battery for up to 661 minutes (11 hours).

Which? Battery life for 7-inch tablets (click to enlarge)

In the small tablet rankings, the Apple iPad Mini is on top with 783 minutes of battery life (13 hours)—some three hours more than the next best challenger, the Amazon Kindle Fire HD, which scored a respectable 591 minutes (9.8 hours). Third was the Google Nexus 7 with 550 minutes, around 9 hours and 10 minutes.

Why do Apple devices lead in battery life? Apple's tight control over hardware and software helps. When multitasking under iOS, most apps are suspended in the background so they don’t zap your battery; on Android, apps have the freedom to continue running in the background and using up more computing resources and battery.

Recent studies also show that ads in free Android apps such as Fchess and Angry Birds take a toll on battery life, as they spend under 25 percent to 35 percent of their energy on game play, but more than 65 percent to 75 percent on user tracking, uploading user information, and downloading ads.