Mac book pro for sale (parts)

Don't sell yourself short. A computer that will turn on and run, but only on power adapter is NOT a "for parts" computer.

What you described is a computer that is "working, needs battery."

(but as everyone has said, this is not the appropriate venue for its actual sale.)

That isn't something you can do on this site but you may want to try eBay, Facebook, Craigslist or other sites that allow sales listings.

You can try local or online, but in either case, this is not the right place for it - we only help with techical problems and it would violate the rules here to share private information - sorry.

You should make sure to use the instructions in the following Apple article to properly prepare the Mac for sale:

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

FYI, if the laptop utilizes a hard drive, then before erasing it you should make sure to enable Filevault and let the encryption process complete. Once the encryption process has completed, then you can perform a simple erase of the physical hard drive. This will ensure that your uncle's personal information is no longer accessible to anyone. If you cannot enable Filevault, then when you erase the drive make sure to select the "Secure Erase" option so that you write zeroes to the whole drive in order to overwrite all data on the drive to make sure your uncle's data is not recoverable. Unfortunately Apple's article assumes Filevault is enabled or the computer is using an SSD.

If the laptop is using an SSD, then just follow the instructions in the Apple article as written since even a simple erase will destroy all data on an SSD due to how SSDs work.