I don't think it's so much that the battery fries. I think it's that moisture remaining on the protection circuitry inside the battery doesn't allow it to operate properly. I once dropped a phone in a river and it sat there for about 5 minutes until I realized I didn't have my phone in my pocket anymore. Went back and found it, but wasn't able to take it apart until about 40 minutes after the fact.
I took everything apart and dried it as best as I could. After everything was dry, I tried to power back on, but it wouldn't. I took the battery apart and found that there was still quite a bit of moisture inside, so I dried that all up too. Mind you that this was when "battery" meant the entire plastic thing that you'd attach to the back of the phone, not like now where it's just the actual battery itself with protection circuit.
After I dried up the battery completely, I gave it a charge and the phone powered back up like nothing was wrong and has worked ever since. The phone is now about 9 years old!
Moral of the story? I would say to try a new battery that's known to work, if available, to rule out the phone being fried. If you're up to it, you might even remove the labeling around the battery to see if there's any moisture still in it. Also, observe for signs of corrosion as these will most certainly cause problems.
While on the subject of corrosion; not every time there's corrosion will something be dead. I've cleaned corrosion off circuit boards that weren't functioning properly after which they worked fine again. This isn't to say that corrosion won't permanently damage anything, it can and will if left on there long enough, but cleaning it when it's discovered can certainly help out.
Hope this helps someone.