Are my charging issues due to my 6p's charging port or the battery?

I purchased a "new other" Nexus 6p on eBay, really it was used but I realized that a little too late. Anyway, the 6p I bought was taking a very long time to charge. I thought that the charging issues were due to the fact that I didn't have the correct wall charger. I only received the charging cable but no type c wall charger. By the time I ordered the correct charger, I realized that wasn't the issue & by then it was to late to return the phone. I'm still hoping I can possibly resolve this issue by replacing the charging port or battery. Currently the phone takes 4 to 12 hours to charge, but doesn't seem to drain too fast. Now that I'm going through the details in this post (& kind of thinking out loud) I believe that there might be a problem with the charging port. Has anyone ever experienced this problem & if so how did you resolve it? Am I right for thinking my charging port is the issue or did I miss something regarding the battery? Thank you and I appreciate any possible feedback in advance. Happy new year everyone

P.S. I would recommend to anyone buying a phone on eBay to make sure they include the right wall charger. I almost never use eBay so that was my mistake, but I hope this helps others.