If these battery usage tests performed by GSMArena are accurate, then the Samsung Galaxy S4 will have some very promising battery efficiency. They got hold of the I9505 which is the Snapdragon 600 version of the device, and initial results suggest the phone could last almost three days through regular use before needing a charge. If true, that's a remarkable achievement with its 2,600mAh battery. Much of this will probably be energy efficiency enhancements in the Snapdragon 600 chip and Samsung's new display. So far, the SGS4 scores near the top of the charts although, of course, it is bested by the Droid RAZR MAXX series. Here's a quote with some of the details of their results,

The Galaxy S4 posted an impressive time in the web browsing test, the usual Achilles heel of AMOLED-based phones. It outlasted an Android 4.1.2-running Galaxy S III by just over two hours.The HTC One managed an hour more with a smaller battery (2,330mAh), but the slightly smaller LCD sure helped.

Video playback is typically a strong suit for AMOLED screens, but the Galaxy S4 doesn’t really improve much over the Galaxy S III. Still, for a 5” 1080p screen that offers brilliant colors and contrast, over 10 hours is a pretty impressive score.

The Samsung Galaxy S4 is a good performer in the individual categories and thanks to efficient standby, it scored a very respectable endurance rating of 63 hours.
Keep in mind this is using GSMArena's aggregate scoring method which supposes you will perform an average of one hour of calling, web browsing and video watching every day. Realistically, this means that even the heaviest users should be able to get through a full day on a charge. You can see more of the individual results at the source link below.

Thanks for the tip, wicked!

Source: GSMArena