If it getting wet on the passenger floor board it's the ac evaporator drain line that's loose or plugged. It could also be coming from under windshield that's where the air comes into the car. Check if you have leaves or debris blocking the area or can cause the water to go into the vehicle. That's what I would check first
I believe that they had an issue with the iPhone 6 or 6s try putting a small magnet next to the camera and see if it fixes it if it does it needs a new camera. I would like to see what happens before I can give you a better diagnosis.
If it works fine with the original battery but doesn't work with the aftermarket ones I would have to say the batteries you bought were probably not the best quality. I buy my batteries from fixez.com and I haven't had any problems with them. They even have the original to chip from texas instruments. It's what tells the battery health and percent of charge. It can have issues if you have a cheap battery.
All iPhones from believe the xs will show its not an original battery and battery health won't show either. It doesn't matter if you try to vs1 it won't work. Apple did to discourage aftermarket repair so the customer will want to take it to an apple store. The last phone that will work is the iPhone X I believe or possibly the XR . Any older phones will work fine.
Look on YouTube. There are multiple videos showing how to change the volume switch. I would watch them all and pick the best one and keep the video on when you are repairing your phone. You can pause and make sure you are doing it correctly.