Well, mine is vented now. Found the "plug" in the trash and put that in the negative side. pulled the existing elbow joint out of the old battery and stuck it in the new one and connected the hose. Who knows if it will make a diff? My current (BMW OE Exide) battery was not hooked up for 6 years and there was no damage to the compartment. But better safe than sorry. Didn't have to buy anything else, but did have to go back in and do it right.
2004 330i E46 with ZHP performance package and cold weather package