One of the big criticisms of stock Android has always been thgat the some of the basic niceties are missing. One of the most prominent of these is simple: the inability to show the battery level as a percentage.
It's a common tweak from the likes of HTC, Samsung or Sony, meaning you can see the battery level at a glance, rather than just as a tiny icon. On stock Android you normally have to swipe down to get the fuller picture.
Fortunately, the option to turn it on lives in Android 6.0 Marshmallow and it's easy to enable in 10 seconds if you know what you're doing.
It lives in something called the System UI Tuner, which is a hidden developer feature that needs to be enabled. Google has hidden this in Android because the features aren't final, and there's the declaration that some of the features might be removed in future Android updates.
Firstly, to turn on System UI Tuner, you'll have to enable the developer options on your Android 6.0 Marshmallow device. To do this, head into Settings, About Phone. At the bottom of the list you'll see the "build number" for your device software. Tap on this repeatedly and it will unlock the developer options that will be added to the settings menu.
Once you've unlocked the developer settings, you'll be able to enable System UI Tuner. To do this, swipe down the Quick Settings panel and you'll see the settings gear icon at the top of the display. Press and hold this.
After a few seconds, the System UI Tuner will be enabled and also appear at the bottom of the settings menu. Once it's enabled, a spanner icon also appears next to your settings shortcut gear.
Open up this menu and you'll find a range of options. Toggle "show embedded battery percentage" and you'll get the battery figure added to the icon, so you can always glance at it.
We've done this on the Nexus 6 and Nexus 5X, but we suspect that outside of Nexus devices you probably won't have (and won't need) access to System UI Tuner.