Hello. My name is Michael. I can help you with your question.
Battereries are extremely sensitive to moisture. It's very likely that the moisture itself damaged the battery - even if it didn't become "wet". Batteries have sensors I them that sense moisture and if to much accumulates, it will render the battery useless. This is for several reasons, including safety. Fortunately, replacing the battery with a new one should fix the issue, and it's an inexpensive fix. What I am linking you to is a Canon original replacement because it is what I would buy. Third party batteries are cheaper, but I don't recommend getting one since, in my experience, they vary greatly in terms of quality.
Please let me know if you still have questions.