[Q] swollen battery screen flicker any ideas? topic

i recently persuded my mom to change her phone today and took her old SG3 of her because the screen was flickering and also the battery expanded i had feeling ti the was the internals of the phone playing up so i decided to take apart my old SG3 with its broke screen and put my internals in to her one but i have noticed that screen still flickers. anyone have a idea what it is it cant be the battery if its gone through 2 already so it has to be something with the screen doyou guys have any ideas or had a similar issue?