I just replaced my E92 battery yesterday. The car has just had it's Fifth birthday (registered Dec 2006.
I bought the car recently and thought that the sluggish battery was due to the fact that it had been sat on a cold forecourt for months. The battery was lucky to do 11 volts when cold, so I bought a Bosch model 96 4 year guarantee battery to replace it, from Carparts4less.co.uk
Cost of battery, 71 UK pounds, good I felt.
I also bought a cable from www.bmwcables.co.uk
to do the registration, which cost another 25 pounds.
The result was good, and the registration below was particularly interesting. It worked first time, and also explains the difference between black and white batteries (mine was white conventional lead-acid), the black ones are the glass-mat ones which are newer tech.
This is from DIS software, which is used at the BMW dealerships, so it should be the last word on whether we need registration for a new battery....
Not only that, if the battery is different, such as capacity, to the old one, then it recommends the further step of recoding as well!!!!
I haven't tried that yet but I have the Progman software working too so I might.