Although I've seen enough comments on other batteries (the Interstates and East Penns etc, even Walmart's) that I wouldn't pay Autozone's price again, when my first 49-DL died it was nice to find that the local Autozone will readily honor the warranty and had my purchase record in their database. Another thing is that they fortunately didn't have any confusion when it came to which Duralasts would work. When I bought the first one, they already knew the 49-DL would work, and that's what they had in stock and recommended. So much for the website....
The battery compartment in an e39 trunk has two or three screw holes for the bottom clamp, to handle batteries of different lengths. When I bought my 49-DL, it looked "close enough" dimensionally that I didn't even bother measuring. One thing I did notice is, it's somewhat lighter than the original BMW unit.