Until recently, this phone still had Android 5.0.2 (Lollipop) on it, which meant that the power-saving app was able to toggle power-saving mode without requiring special permissions. However, since my upgrade to Android 6.0.1 on the phone (Marshmallow), this permission is no longer granted. And so I needed to grant access to the power-saving app, to restricted settings on the phone, via ADB USB Debugging.
Today was the first time I ever used the ADB Drivers on my Linux laptop named ‘Klystron’.
The app in question tells its users, what commands to give the ADB shell, so that it will gain the ability to toggle power-saving on and off, without having to display a GUI automation, which under Android 6.0.1 will fail anyway. This is listed by the app, when tapping on the section “Set Up Hiding System Bars”, and the next section only becomes selectable, once the app has detected that the ADB-action succeeded. I have followed the instructions, and the app now works fully, so that together with my NFC Tags, I can turn power-saving on and off easily again.
There is a caveat to setting up USB Debugging on the phone, which I needed to overcome before reaching success. It is a two-step process, not a one-step process, which is best-described here. Obviously, I do not recommend disabling the feature of Developer Mode again, because under Android 6.0.1, along with USB Debugging, the feature can be toggled off again with a GUI-button.
Before I had realized this was a two-step procedure required on the phone, I had erroneously thought that my failure to accomplish this was somehow due to the Linux ADB Drivers. However, those seem to work flawlessly.
Now that the power-saving app works fully, one side-effect which anybody should know about, who might want to use it, is that it will apply all of the features in one batch, that its author suggested it should apply. This includes hiding the entire Notification Bar, not just the GUI-nuisance I once associated with using it. Relax, the notification bar can be made to reappear temporarily, by swiping down from the top of the screen, after which it in turn can be made to expand into the usual list of notifications, by swiping a second time, before it hides again.
And for the long term, once the app is deactivated, that notification bar just reappears, as if nothing had ever happened.
(Edit : ) Actually, I have just learned that even if we have completed “Set Up Hiding System Bars” as described above, it is not necessary for the operation of this app, actually to select “Hide System Bars”, the whole point of which was apparently, to hide the Notification Bar. Instead, once we have used ADB to grant privileges to the app, it will recognize that it has said privileges, and will enable Power Saving Mode, optionally without hiding the Notification Bar, which on my phone stays an agreeable shade of gray, and does not look ugly.