Water under the battery

This can be from overcharging of the battery. Do you smell a strange odor near the battery too? Almost like rotten eggs. If so the alternator is overcharging the battery and the battery acid is coming out the battery vents. Put baking soda on the area to soak up and neutralize the acid (water). It's highly corrosive and will damage the metal battery tray. Have the charging system checked and replace the battery. Hope that helps! Jim

Oh and once the baking soda has absorbed the acid, rinse the area with lots of clean water. Jim

As most of these were under the rear seat cushion it is very important you make sure it is only water, if it is then you need to hunt for water leaking into the vehicle, could be a plugged door drain or sun roof drain. If it is battery acid then the area needs to be treated with baking soda and vinegar then completely washed away, make sure there are no possible sources of ignition near by. Then have the complete charge start system checked by someone that knows how to do computer controlled systems and repair as needed. Make sure the vent hose is connected to the battery vent fitting.

The battery compartment has a vent tube for evacuating gasses and moisture from that area inside the car's occupant cabin. Your vent tube is clogged. Just run a cleaner through it.