Share your experience!
So while it is charging it also drains?It could be related to intense using(the phone getting very hot,in which case it will not charge anymore,even if connected to wall socket or USB).
Try to remove any kind of battery savers,task killers.Force shutdown your device after that(press the little button on the back of your device).Turn it on normally after.
I do not think you can see if the phone is charging.If not charging,you can only see which apps drain.Try to look on google play for some kind of hardware app.
Well,are you willing to try a software repair via SUS?
http://www.sonymobile.com/gb/tools/update-service/
Yes,at least 50%,but you go for 70-75%.Good luck.