I have this model laptop vaio sve14aa11w i think its cpu can be upgraded if it can what is the latest cpu that it can...

are the parts from all 3 models compatible with each other like the battery case and screw wholes I have a 1396 model but...

I'm not really sure how, you might be able to search for compatible and higher quality speakers for your phone other than that I don't think you can do anything if you think the phone's volume has decreased since you first got it then cleaning the speaker might help out or just replacing it entirely

I don't know if this will help but I had the same problem I think it's just because Xiaomi just wanted to save some money so they cheaped out on the case and buttons I would recommend getting a new case its the easiest solution instead of replacing the buttons and you can even get a new color and if the phone had any scratches it won't have after getting the new case the overheating problem I had to most likely it's just the batteries life has reached its end either that or the charging port is starting to wear lastly te button still doesn't work after getting the new case make sure you clean it if it still doesn't work then your gonna have to replace the buttons flex cable but most of the time its just dirt that's stopping the button from working