so I own 2 bmws an E70 x5 and my z3 both of which I only got with 1 key. So the x5 battery finally died so I thought I would get a spare key for each car. Phoned around the car key companies and it seemed the recommendation was to buy from main dealer as they are complicated and the cost won't be much different to main dealer. So trip to main dealer today armed with 2 log books a utility bill and a photo driving licence and my keys. The x5 flat key battery was replaced fortunately it has comfort entry and the battery can be replaced otherwise that would also have been another new key as the batteries are not replaceable in the standard entry key !! Anyhow 2 new keys ordered one standard x5 entry key and one new z3 key £330 if you please. Had I bought a spare comfort entry key that's a whopping £350 on its own as the old missing key has to be removed from the ecu. Moral of the story get a spare key with the car.