I want to replace mine with the same type and style as the original. It just goes well with the entire under hood experience! Interesting note about the OEM weight, as nimble as these cars are, maybe its neccessary to keep all 4 wheels on the ground? (LMAO)
EDIT:
Automotive / Truck Batteries - Mega-Tron Plus - 85 Months - 640 CCA
This is the interstate battery (MTP-H6) they reccommend for the XF on their website. Its also the same one for the MB SLK320. Looks exactly like the one in my car now.