Is it possible to configure the phone to charge when the battery left X amount of juice? Illustration: I plug in an android phone to either a power bank or a charger. However, I do not want it to start charging immediately. I want to configure the phone such that when the android phone battery reached certain level (e.g. 35% or below), then it will start charging.

So, is it possible to configure the phone to charge when the battery left X amount of juice?
Depending on the kernel the phone uses it may be possible. If you use a kernel with the ability to change the charging power like the Boeffla kernel then you can create a profile in the Configuration app that comes with that kernel and set the maximum power usage to 0mA. Then you can use Tasker, an app you can get from the Play Store, to send an Intent to that app to change to a specific profile eg. the one which changes to normal charging power and you're done.

As I have written: Check your kernel. If you don't know about anything I have written than just plug your phone in when you think it's time.