Are there parts compatibility issues w/ the freebie at the 4S launch?

My son's 3G got stolen and I upgraded him with the 8 gig freebie available last year.

It got wet and I had it working again, but it traveled with him and something happened to it and I can't quite get it back to normal.

Ports that work in my 3GS won't work in his, and he needs that 0435 battery that's hard to get a hold of right now. Is the port issue more related to the battery or the motherboard or both?

My issue is that his reception is awful except with the port that is currently in my phone--but that port won't charge the battery that works in his phone. My phone seems to accept either.

Right now it's acting like it has a bad battery (again) and I just replaced the port with a new one. Should I keep trying to switch out the ports? Or should I focus on the battery?

Thanks!