My 2011 GSA oem battery was giving up the ghost, but apparently not quite dead enough for BMW to replace under warranty (although it tested at 9.8 under load). I read several threads suggesting the Odyssey PC625 was a good replacement option, so decided to give it a go. With some help from JVB, and a utility knife and dremel, the Odyssey fit right in. Needless to say, I am very glad to have this powerplant with our daytime temps hovering in the teens.
GSA battery, a stock GS battery, and the Odyssey 625.
Remove this tray and the larger standard GS battery fits.
Some trimming of the fins and the PC625 fits.
But a seat bar trimming is in order.