The Xperia Z4 Tablet has a 6,000mAh non-removable battery inside, a hefty unit for any tablet, but it hasn't changed since the same cell was included in the original Tablet Z many moons ago.

Considering that Sony has upped the display – the biggest battery drainer – it begs the question as to whether the battery should have been improved as well.

The Xperia Z4 Tablet has a similar battery life to the 17-18 hours of video Sony was stating at the Z2 Tablet launch.

Sony should be praised for delivering that kind of battery life considering the sharpness of the Z4's display – you'll be able to get through a long-haul flight's worth of movies and not have to worry about the tablet dying on you.

We ran the Nyan Gareth video – our traditional battery test of a 90-minute straight video at 100% brightness – and managed to get a score of 79%.

Considering that the Xperia Z2 Tablet scored 72% this is quite impressive, and Sony has clearly made some improvements under the hood to obtain this level of performance.

Sony Xperia Z4 Tablet Review

I then ran the test again at 60% brightness, as personally I'm willing to sacrifice a little screen brightness for an extra film's worth of battery life, but I only managed to get a score of 81%, so it's not really worth dropping the brightness when watching video, as you won't see a big difference in battery life.

General battery life proved impressive as well. I had the Z4 idle in my bag idle over a weekend and I didn't see more than 20% of the battery drain, even though the tablet was connecting to Wi-Fi and receiving notifications.

It just proves that the big battery drainer here is the display – although it's worth it for such a beautiful-looking screen.

I did find charging an almighty task though. Tablets usually take quite a while to get up to full charge, but using my normal phone charger made for a particularly slow process. Fast charging technology would be a nice touch here.

Also it's worth noting that there's no wireless charging option, which would have been a welcome addition for those who don't want to be restricted by a cable.

Interface

The Xperia Z4 Tablet comes with Android 5.0 Lollipop, and you get to use all of Google's freshly implemented features.

However, Sony's UI is as prevalent as ever, which will disappoint some. It doesn't really add much to the Android experience, and I can see how it may confuse new users. Sony isn't likely to drop it though, so it seems that we're stuck with it.

Sony has also confirmed it will bring Android 6 Marshmallow software to the Xperia Z4 Tablet, but it's not ready yet. That's a disappointment considering Marshmallow came out in October 2015 and it's still not ready.

Sony Xperia Z4 Tablet Review

Sony has taken inspiration from Google's Material Design, but the new design language isn't fully implemented; I like the new minimalist design Google is offering with stock Android, but Sony changes all the icons to its standard look, which puts a dampener on the user experience for me.

One of the big new features of Android Lollipop is lock screen notifications, and these come in very useful. Instead of having to swipe down to read your latest goings on you can just hit the power button on the left-hand side and everything is there.

Sony Xperia Z4 Review

Tap and unlock to view the notifications in more detail, or just swipe them away if you're not that interested. It's smart, and it's one of the nicest Android additions we've seen in a few years.

With Samsung dropping a lot of its bloatware apps from the Galaxy S6 and Galaxy S6 Edge, Sony is becoming potentially the biggest culprit for filling its devices with largely useless services.

Sony Xperia Z4 Review

Some of the pre-installed apps are useful of course, such as the PlayStation app – having this installed ready and waiting makes sense, especially with the Remote Play feature on the new tablet.

But there are also the likes of Sketch, Xperia Lounge, SocialLife and Lifelog, which I find utterly useless and which take up precious storage space – and the worst part is that none of them can be deleted.

Sony Xperia Z4 Review

Sony really needs to understand that people don't want to waste their precious storage space on apps they're never going to use, and filling its devices full of these will make people look toward stock versions in the future.

Sony Xperia Z4 Tablet Review

The slate also comes with a few third-party services pre-installed, including some useful ones such as Facebook, Spotify and Skype.

The addition of the Android Lollipop features is welcome, but Sony has some real work to do before I want to shout from the rooftops about its tablet software. It's a bland, functional interface that harks back to darker days of tablet design – although it should be said that it is thoroughly usable.