The battery life is quoted by Sony as having 16 hours max talktime, 820 hours of standby, 110 hours of music and seven hours of video playback. Of course, in the official documentation, that's all followed by a load of asterixes to warn you that was all achieved in laboratory conditions.
And unless you're a scientist, you won't be using yours in a lab, which makes the whole thing pointless.
There is no general rule with a device like this because we all use them differently. It's not as easy as just talking about a phone these days. The way to approach it is this: if the device is hammered, then the battery won't last. If you take some care in your use, you'll do well in the course of a day.
We found that it actually managed to last quite well. At 3050mAH, it's smaller than the Galaxy Note 3 and has a bigger screen to power. And yet, we found it performed as well as the Samsung device, if not better.
We took our Xperia Ultra Z off charge at 7am. We did that very modern thing of checking Facebook, Instagram and Twitter while the kettle boiled and read a few emails that had come in overnight.
We then left it an hour or so and when we picked it up, the Xperia Ultra Z was still showing 100%. This was with Gmail and MS Exchange pushing emails through all the while.
At about 8:30, we fired up TuneIn Radio and connected it to the car via Bluetooth and drove around with Google Maps navigating us for about 20 minutes. The screen was on the whole time, but we still had 89% remaining when we got back.
Over the course of the next few hours, we had a good intensive play. Downloading apps, playing with the camera. We took about 12 photos, shot a couple of small videos, watched a whole episode of Doctor Who on the screen, 'threw' a few photos to the telly, spent an hour or so browsing the web and made one 14 minute-long phone call.
By the time we went to bed at 10pm, the battery still had 32% remaining. It's worth noting that a good chunk of the day was spent travelling on the train where signal goes up and down like a crazy yo-yo so the Xperia Ultra Z would have had to work extra hard.
We were actually really impressed with that. We'd consider ourselves fairly heavy users and if you were to curtail your usage, you'd easily squeeze out two, maybe two and a half days out of that battery. It's worth also pointing out that that was without Sony's Stamina mode enabled.
That acts as a smart throttle of data services to keep the battery as high as possible. Expect even greater things if you enable it.
Here's where we would normally bemoan the lack of a removable battery. But we won't here. The fact that this seems to cope so well makes it less of an issue. If only other manufacturers would follow suit.