Oh-kaaaay I think my luck with the Duralast 49DL is done. I went through two in 16 months. Both completely died within a couple days after coming off a Deltran battery tender (same one BMW sells I think...) with readings of 12.6 V. The second one had a reading of 7 V when I took it to Autozone to test. They refunded me $95, I took that and bought the H8 SuperMAXX at Walmart ($98 here in Eugene). The SuperMAXX has substantially more heft than the Duralast -- feels closer in mass to the BMW original. It also has vents on each end like the genuine BMW batteries do, with a small plug (still attached to the pos. terminal cap) that you use to plug the vent you will not use (the one on the aft end....).
I've been through the check-out routine for parasitic drain and will do it again to be sure, but last time I checked, after 16 min. my car goes into sleep mode and shows a current drain of between 0.02-0.05 amp. Is that enough to kill a battery in a car that's not driven for say, four or five days? I typically put the car on the tender (using underhood terminal connectors) once or twice a month.