MadAdey
Money List Winner
I would advise get a pro to do it and do not DIY. All right changing a battery on a cortina in the old days. But now, you have spohisticated alarms, and immobilisers, for example, that need a constant link, and disconnecting a battery can screw this up.
There are ways around that problem, but you are spot on with that statement. On my 5 series I know if you change the battery you need to have it registered to the car by a computer at the stealership or there is a risk of getting random problems. It's nice having all these fancy extras but they can make car DIY a right pain.