My device care in setting is giving a warning about my battery life. But it's so hard to go to a service center in this covid 19 situation. So if possible, please help me. 

 What will happen if I overcharge my phone?

I recently noticed that  Samsung will erase everything in my Samsung account if I remain inactive for long time. If it is true than will Samsung delete my contacts? And when it will happen? 

How can i clear the empty and junk files of my phone?

will Samsung consume more power if i upgrade it from android 9 to 10?