1. Were you having battery drain problems prior to it getting wet?
2. Are you unknowingly using the device more than you were prior to it getting rained on, as in checking it often to see if it still works, etcetera?
3. Do you have AppleCare +?
Anyway, it's hard for any of us to answer your question. All we can do is advise you to monitor it over the next few days and see if it improves. If you have AppleCare +, you might want to consider using it.