any good shop for repair?

my wife mate 8 seems the volume button is a gonee, SC  qoute "back cover with side keys" 300+

my battery having issue after traveling and heavy usage of gps together with powerbank for fews days.

encounter phone battery drop faster when left 20%, after use a while direct drop to 10%.

i uninstall un use apps , clear cache/data maps, fb, wechat/whatsapp etc.
yesterday when battery left 17%, i play clash royale for a match bout 3min, battery drop to 8%, and when i play 2nd match, jus few second i c battery is at 4%, and 2 sec later shutdown.

my friend was shock also and suspect battery faulty. but when fully charge it can last until i off work around 5 o 6pm. but battery drop faster than be4.

any advise?

mind telling which shop? thanks

been using this phone for over a year now, only lately feel the swell through the rubber casing.

btw just now i charging the phone for nearly 3 hours, the phone could not be charge beyond 98%. need to change the battery i guess..