WhatsApp icon greyed out

Problem:
Yesterday my WhatsApp icon on the home screen had greyed out. It had turned into that translucent grey colour and it seemed to be not responding. The app would not launch even from the Application List, obviously.

Solution:
Turn on the backup
Settings > Backup > App + Settings > Backup Now

Cause:
I remembered that the last activity that I was asked by the OS to do was to backup. It seems I had started the backup process, but it was too slow, so I switched off the Wifi and went to sleep. I just restarted that process of backup and WhatsApp icon was in its normal state in around 10 minutes. It looks like WhatsApp is one of the apps that performs a backup during this operation and it remains in an unusable state during the initial part of its backup process.

Battery

"How is the battery life after 2 years?", I have been asked that many times in the recent few weeks. I still manage to tell them that on 'Batter Saver mode, it lasts for almost 2 days'.

I see videos on YouTube and listen to songs at work. Other than that the phone is used to send and receive phone calls through the day. I seldom use Facebook on the phone. WhatsApp is turned on at an average of 2 hours per day. The screen brightness has been set to Automatic.

The OS takes care of the battery management and that is the reason why the phone cannot be turned off while the battery is charging. You see, the OS has to be running to ensure that the battery is optimally charged and used.