AerocomRadio

1. How long have you've had the phone ? 2. Case To Case Basis ... how you charge it. 3. Yes it's Lithium Ion Battery and usually in this case you can charge it anytime low bat full bat. However, sometimes when you are charging from Point of Connection to the Charging Circuitry to the Battery. Could be a Flex issue or connection issue inside that's if it's a built in battery. However in this case seems like the battery has taken it's toll or you just got a lemon. Usually Lithium Ion batteries last 3 years. I have a Lithium Ion battery that lasted me from 2010 - 2017 and it's still charging and working. So depends on how it's charged. I don't know the history of your charging cycle . Best to give more detailed information. When it was working to the point when it stopped working. Thanks Answer: Replace Battery to isolate the issue.

Rest Procedure, it's a two button configuration to rest the entire Phone. You might loose contacts, pictures passwords etc; are you prepared for this ? Check manual for 2 button reset.

I'm a technician and remembering some of the connectors I believe not, because 1 iPhone 8 back plate is made of glass not your average aluminum. Weird right. As the iPhone 7 is Aluminum there for there's a slight difference in the size of the LCD by milometers actually. Specs iPhone 8 - 138.4 x 67.3 x 7.3 mm (5.45 x 2.65 x 0.29 in) and 148g (5.22 oz) iPhone 7 - 138.3 x 67.1 x 7.1 mm (5.44 x 2.64 x 0.28 in) and 138g (4.87 oz)

Try taking it apart and try the power button while it's apart. If the power button is working when it's taken apart then it's an assembly connection issue. So check the cables connectors and flex ribbons to make sure all connections are connected and not tweak on the side. I'm trying to picture it in my head how you took it apart, however since you did to clean the DUST from the insides. There shouldn't be an issue with the power button. Thanks hope this helps