iPhone has been charging for over an hour but I still see the empty battery screen even while still plugged
iPhone won’t start, empty battery is on screen even when plugged in. How to get it to start?
iPhone 6 Plus
If it won't charge plugged in after an hour, there's a good chance if your signature is correct and you have iPhone 6, the battery has failed.
See this link, but if nothing helps, it's time for either a new battery or a new phone since iPhone 6 is now out of date, no longer supported and can't run the newer iOS versions.
See this --> If your iPhone or iPod touch won't charge - Apple Support