Asus did not release an official battery capacity figure for the ZenPad S 8.0 – but the 3DMark app says it is 4000 mAh which seems accurate given the performance I experienced.
In everyday terms, I think you would be fortunate to last 2 full days with the ZenPad S 8.0. I found that using social media intermittently, watching videos and running our benchmarks drained the tablet faster than I would have liked. For instance, a 90-minute HD video drained the ZenPad's battery by 26%, meaning it can play roughly 5-and-a-half hours of HD video from a single charge. This is not huge, so do not expect to be using the tablet for several days before it will need recharging.
The Geekbench 3 battery benchmark only confirmed this. The ZenPad S 8.0 lasted 6:25, well below the time posted by the Vodafone Tab Prime 6. Clearly, the 4000 mAh battery is just not enough for the high resolution display.