Battery Repair/Replacement and Previous Complete Salt Water Immersion

So, I have a very unique situation. I’m just trying the fix for a friend, more for the learning opportunity because I enjoy taking apart iPhones and the challenge, and this has certainly been my biggest challenge to date.

My friend dropped her iPhone 6S Plus in the Mediterranean ocean while we were on a catamaran in Greece. We were fortunately in shallow enough waters and she was able to dive down and grab the phone. Another friend on the boat was a photographer and had those silicone packs to help dry it out. However, we were on a 3-week trip and this was only 1 week into it. So it was about a month before I was able to work on it. By this time, the salt had begun to rust the inside, but I followed a guide and threw it in 99.99% isopropyl alcohol and it looked pretty good.

I ordered the replacement parts, and according to the guide, I took the registered fingerprint pieces from her old phone and basically while everything was opened, we replaced the battery, the screen, and kept only the necessary pieces.

To my amazement, the phone actually turned on, but the new battery only had something like 15% of a charge to it, and it won’t charge at all. It seems to me that everything else is working, does it seem likely that the charging port may have been damaged (it was working fine prior to having been dropped in the water), and we tried everything, i.e. using an Apple branded wall charger, etc. It wasn’t dropped onto a hard surface, so I didn’t know if that was a common occurrence for the charging ports to get defects from water?

Does anyone make a tool that charges iPhone batteries outside of the phone, just to verify that I didn’t receive a defective battery? And if so where to purchase those?

Thanks in advance for any assistance you can provide!