I claim that any recent smartphone can work up to two days including a few hours of browsing and doing calls, once you disable all (unnecessary) background synchronizations, forcing the hardware awake. At least this is my experience for the Nexus 4.
But reading that the authors phone "used to die with 6–8 hours of moderate usage or sometimes even before that", it seems he had much higher expectations than me. I don't expect a phone to work in "active" mode with screen on for so many hours. I expect it to consume just little power when screen is off and few background synchronizations run, and do not care much about consumption when the screen is on. If you need 8 hours (that is 1/3 day) of screen-on time then maybe your expectations are too high on a smartphone? Additionally you would probably stumble over a power socket in the meantime.