The only real problem I had was the internal boot door wouldn't close because the top of the battery hit it, so I had to cut some support metalwork (the bit that would normally hold the battery tray up) out of the boot compartment floor and drop the plastic battery tray lower to compensate for this. This also meant modifying the plastic battery tray to make it shorter. All in all it doubled the length of time the job took and was a PITA.
Mods required to boot floor to take battery tray in my touring:
So imagine my surprise whilst closely examining my new 325iX touring today
when I noticed the battery was already in the boot! How did BMW do this I asked myself? On closer inspection, they used the same 2 door battery tray but they made a different boot 'door' with a larger bulge in it to accommodate the battery!Part number 8 in the diagram:
The door part number for a normal touring is 51471947874, the part number for the iX's boot door is 51471972454. I hope this useless bit of info saves a lot of time for someone!
**Note: The battery cable on the iX model leaves the battery vertically and goes up over the wheelarch to avoid the boot carpet, although the 2 door cabling can be used if required, like I did. If you are buying new battery cable then I would suggest the iX specific one. That would save even more work. Good old BMW think of everything.
Now ive got to redo it 
PITA x2 
Cos i aint that happy about were it is 
Cheers for the info tho!