Has anyone ever heard of this?

Yesterday, I started smelling something throught the air vents...like a burning smell. So I stopped the car and went hunting. I found the battery was sizzling and venting some fluid out the side. So I replaced the battery right away.

This moring after driving it last night I find a similar situation with the new battery. There was a little adapter and a hose with the battery. The guy at the parts store said that this hose is to attach to some kind of drain that some cars have to vent the battey!

What the heck are they talking about? I have never heard of "venting a battery". But I do know I dont want battery acid spitting on the inside of the engine compartment!

Any clues?

Steve