I've had my Galaxy s7 for just over a year now. About a week ago, it went from 7% to 0 instantly. Now without fail, at 28% it drops to 13%, even if I have it plugged in. After that, it drops to about 3, then dies, regardless of whether it's plugged in or not. I know you can buy a new battery and replace it yourself, but I'm not so sure that's something I trust myself to do. So is this something they can do at the store, or will I need to do it myself?