Why does it take forever to charge an iPhone X?

You may have something that is physically wrong with your phone. How much storage you have used on the phone has nothing to do with how long it takes to charge. If you aren't able to get it to charge over 85% and charging is taking a long time, there could be something wrong with the phone or the charging module or battery, impossible to know for sure without testing things out. I would suggest making an appointment with a Genius Bar at your local Apple store if you have one near. If you don't have one near, then get in touch with Apple technical support and let them know what you have going on. The phone should be under warranty and you should be able to get them to help you out getting the issue repaired.

A 12 volt charger will wreck your phones battery permanentl. Get you’re battery replaced, and stop using that charger!!

Hi

You need to use the mains plug on the wall if you have been make an appointment at Apple store.

Or contact Support.apple.com.

Cheers

Brian🇬-1F1E7;