Inside the Asus Zenfone 5 is an 8.02 Wh, 2,110 mAh non-removable battery, despite the fact the back cover of the device can be removed. The Intel Atom SoC is a 32nm part, so its marginally disadvantaged due to its manufacturing process compared to the latest Qualcomm SoCs, leading to lower energy efficiency.
This seems to have translated to results, with the Zenfone 5 producing a disappointing showing in the following battery benchmarks. Standby battery life, which we don't benchmark, is actually pretty good, so if you're not a heavy screen-on user you'll probably see results that are slightly better than what's reflected below.
The Zenfone 5 comes with several battery saver modes, one of which is labelled as Ultra-Saving Mode that disables network connectivity when the display is off. Another mode called Optimized Mode keeps the network connection enabled but extends the battery life through unspecified methods. The final mode allows you to customize how the battery is saved through controlling brightnesses and disabling certain features when the battery gets low.