Install It If You Can't Fix Your Problems
If you're on Google's Android Lollipop (or god forbid something older than that) and you've been unable to fix your problems, you'll want to think about installing the Nexus Android 6.0 Marshmallow update on your device.
Android 6.0 Marshmallow comes with fixes for various problems with the Android operating system. As Android Police notes, there are over 27,000 commits in the Android 6.0 change log. Many of these are fixes for issues.
Even if the change log doesn't list a fix for your problem, there's a chance that the update will still solve the issue. We've been through many Nexus Android updates and it's common to see an update fix an issue without a mention in the change log.
In particular, we've had Android updates iron out abnormal battery drain (remember what we said about Doze) and connectivity issues without noting them in the official list of fixes.
So, if you've tried everything and you don't want to replace your device with a new one, you might want to give Marshmallow a chance.