Q: Mold and water found in base of battery compartment

After we had spent a considerable amount of money on an unresolved engine light issue and hoping no more problems would arise with our SUV, the next week I tried to open the door with the remote and it didn’t open. I found that the battery was dead when I tried to jump-start it. I had just replaced the battery only 7 months before this. When I lifted the floor mat to uncover the battery compartment, it was molded. I removed the battery cover and the battery and found 2 inches of brown water in the base of the compartment. Also, the other battery that we had kept also had mold on it. Fortunately, this happened while we were at home and not caught out in the heat of this summertime. We can’t figure out how long the water had been there or how the water even got into the battery compartment. We took pictures as evidence to send to Saturn customer care. Can you tell me how the water got into the battery compartment and should we keep the SUV out of rain?