Due in final version, M Android is currently available as a developer preview on Nexus 5, 6 and 9 and has joined the Sony AOSP program. By the release of the final version, the firmware will be updated several times and the next build should add an option that should please the Stock Android users. The display of remaining battery percentage in the notifications bar will be offered natively.

Do not miss: Android M, the functionality of the new version
Android battery percentage M
The battery percentage display finally offered natively.

If you've ever used a Nexus, then you are aware that in the stock version of the OS to display the remaining battery percentage in the notifications bar it is necessary to install a third party application like "Activator percentage "that lets you change the battery icon without root. Without this manipulation, the simple filling of the icon that tells you how much energy you have left, unless of course you go into the settings of the battery.

That said, even with a very good view, you have only an estimate but not the exact number. Fortunately, everything should change with the next build of Android M which will soon be distributed to developers. As evidenced by a recent entry from the AOSP Android tracker bugs, this option will be available soon next build will be distributed before the end of the month, through developers options.