I've had the same problem with a flat battery. My bike will start fine above 40 F; below that I have to be lucky or have it on a tender. I knew the BMW guys swore by the Odyssey battery so I looked at doing what you are doing with a new battery box and refit. I stopped when I went to a motorcycle show and found the CCA ratings to compare the Odyssey with the Yuasa. I think The 545 Odyssey was 185 CCAs and the Yuasa was 220 CCAs. I know nothing about batteries and whether the CCA ratings are the real deal for a baseline measurement.
Please keep us posted as I may be right behind you on the refit.