Battery life
The Transformer Prime is choc-full of selling points; whether it's the Super IPS+ display, the quad-core Tegra 3 processor or the 8-megapixel camera, there are plenty of reasons to be eyeing up the device. Though, in our estimation, none are quite as attractive as ASUS's quoted battery life.
According to the manufacturer, the Prime will run for up to 12 hours when used as a standalone tablet, and that figure rises to 18 hours with the keyboard dock attached. The purported numbers are higher than Apple's claim of up to 10 hours from an iPad 2, so we've put them head to head in a battery rundown test to see who comes out on top.
For the purpose of this benchmark, all tested tablets are fully charged, all background applications are closed, Bluetooth is disabled, Wi-Fi is enabled but not connected, and screen brightness is set to 50 per cent. The Transformer Prime is set to its "balanced" power profile, and we then repeatedly loop a 720p movie clip until the tablet runs out of juice - and we're using the same movie clip as we do for laptops, allowing you to cross-compare run times.
Sounds easy enough, but the limitations of both Android and iOS are such that there's no built-in function for looping video; the respective media players really are that basic. However, in true tablet fashion, there is an app for that, so we're using mVideoPlayer for Android and LoopyLoopy for iOS.
With the dock connected, the Transformer Prime just keeps going and going and going. Let me tell you, testing battery life on devices such as these ain't a whole lot of fun, but 16-and-a-half hours of repeated 720p movie playback is simply outstanding.
Even without the dock, the Prime managed to run for just over 10 hours, and though that's just shy of the iPad and iPad 2, we reckon the Transformer Prime display is slightly brighter at 50 per cent.
Over 16 hours of battery life is terrific, but having high capacity batteries does introduce a small disadvantage; such devices typically take longer to charge.
In this test, we take our flat, depleted tablets, plug them into the mains and time how long it takes to restore the integrated batteries to a full 100 per cent charge. ASUS's Transformer Prime has both a 25Whr and a 22Whr battery to replenish, and it takes almost six hours to do it. The tablet portion alone, however, is able to recharge fully in three hours and thirty-nine minutes, which is comfortably quicker than the iPad 2's four-and-a-half hour charge time.
Why is the iPad battery visibly inferior to that of the iPad 2? We think it has more to do with the condition of our tablets than the internal battery specification - our first-generation iPad has seen regular use for over a year, and the condition of its battery most likely isn't what it once was.
