The Xperia Z5 comes with an 11.2 Wh (2,900 mAh at 3.85 V) non-removable battery, which is a slight reduction in capacity compared to previous Xperia flagship devices. Sony claims this battery is capable of "up to 2 days" of battery life, but in my general usage (and this shouldn't come as a surprise to anyone), this definitely wasn't the case. The Xperia Z5 is a one-day phone at best, and I put that down to the power requirements of the Snapdragon 810 SoC.
I was actually pretty disappointed in the battery life of the Z5. Previous Xperia devices had terrific stamina, and that was a standout feature of the handset that made it worth considering over other devices. The Xperia Z3 in particular was a fantastic performer in terms of battery life. With the Z5, however, the smaller battery capacity combined with a more power hungry SoC has relegated this device to merely average battery life, as you'll see in the benchmarks below.
As you can see, the Xperia Z5 sits in the middle of most battery life charts, below the great battery life of the Xperia Z2 (especially in web browsing). This represents a disappointing regression in battery life compared to past devices.
Charge times aren't amazing either, with Sony failing to integrate a good fast charging system into the Xperia Z5. A full charge takes more than twice as long as the Samsung Galaxy S6 from the included charger, while burst charging is typical of a device that doesn't support Quick Charge 2.0.