Battery Exploded
 

My girlfriend has a 2005 Mazda Tribute, last night the battery exploded. Had it towed to the dealership, unfortunately it sat all night and the acid didn't get neutralized until this morning.Dealership is doing the work under warranty and they are also going to paint the underside of the hood since it blistered. According to the dealership the neutralized everything this morning.

My question iswhat would cause a battery to explode (she wasn't jump starting anothervehicle) and whatelse can the aciddamage in the engine compartment.