I replaced two batteries with AGM, one on a 330xi which originally had a wet cell and the other on my X5 which already had AGM. Both new AGM batteries as well as the old one had vent tubes so not sure why you guys are saying AGM doesn't have it. :dunno:

Only one poster mentioned no venting...my last AGM replacement and the new AGM replacement both have a vent hole for the vent tube, albeit the 'vent hole' had to be punched out in both situs.

Most Batt info sites still rec'd 'venting' of some kind, via the tube or louvers eg a boat, et al.

IIRC, excessive charge will allow for pressure build up in the batt case and that 'pressure'/fumes need venting, esp in an enclosed space such as the rear cubby where these batteries reside. My 50Cts...
GL, mD