My phone takes 8 hours to charge

@funnyapollo there are multiple things that can cause this. First thing to check should always be the software. Make sure that your software is up to date and clear the cache on your phone.

The other issues are commonly related to a bad USB part or charging board. Since there are no schematics, replace that board. It is inexpensive and fairly straight forward to change. Double check the ribbon cable form the charging board to the main board. Make sure there are no rips or tears and that the connector is properly working. I would also consider to replace the battery.

If all of that does not resolve the issue, it is possible that your motherboard charging circuitry is giving you an issue. For that your will need the schematic, the board layout file as well as the tools and skills to perform a boardlevel repair.

To work on your phone and since iFixit does not yet have a guide for this, use something like this video. Charging board and battery are readily available at many online stores.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!