New TT battery box full of water

Opened up my plastic battery box on my 2 month old TT, and found it was full of water...there are a couple of ventilation slots on the tp so I guess it got in there.... I was worried something could short out or something? I drilled a half doz. holes in the bottom of the box so water will drain out.... Is this unusual? Why wouldn't the box have some sort of drainage? It sits right behind my propane tanks.