Culled from vendor's websites (their claims, not mine):
The Braille unit is superior on paper to the Odyssey for the 15lb size:
Locating suitable Z4/E46 brackets are the issue, not many choices. My opening post has one.
Odyssey explains some terminology:
Cold Cranking Amps: For all the power, durability, and life of our technology, the cca ratings can seem disapointing. That's because the cca ratings are often misunderstood. Odyssey batteries are SLI (starting, lighting and ignition), so if you are looking for a starting or reserve battery the cold cranking numbers can be irrelevant.
The "standard" cca test measures the output of a battery for 30 seconds of crank at 0 degrees with the ending voltage of the battery being 7.2v. Some companies use 15 or 20 seconds and some companies use 32 degrees which can make for better results.
A vehicles starter isn't designed to withstand 30 seconds of cranking so we feel the batteries starting power is more important. The Odyssey part numbers represent the 5 second cranking power of the battery.
The PC680 is rated at 680 amps for 5 seconds, 595 amps for 10 seconds, and 525 amps for 20 seconds. Cranking power is even higher for the first four seconds. Similar sized lead acid batteries are only rated at 180 - 220 amps.