Water damage leads to battery not charging.

I have been unlucky enough to encounter minor water damage on my 4 month old MBP. I say minor because I spilled water on the left-hand side of the laptop. I took all the standard measures to dry it out, and after turning it on, I had issues with weird fonts or being stuck in caps. I took it down to the Apple store to have them tell me they detected liquid damage and it was no longer covered. Low and behold, I turned my computer on today (next day) and it was functioning fine. I am typing on it as we speak.

The only problem is that my battery is not charging. It is plugged into the wall and works this way, but the charge is down now so that it will not function without being plugged in. The light is a dimmed green. I figure 3 things can be wrong.

1. The charger was somehow ruined by being plugged into a moist port.

2. The port was corroded and no longer functions.

3. The battery on the inside is shot due to water damage.

Which of the three is most likely, and what is the most economical fix?