yes it will need to be charged, however, i think the case is that you'll need to have the key coded with a BMW GT1 or DIS system otherwise the car will not recognize it. When you use you're old beat up key to start the car, the security system releases its hold on the car. The car stay active for about 10minutes after removing the old key and after that is when i assume the new key stops working.

Have it coded! However the X5 only accepts a maximum of 4 keys before it will no longer allow new keys to let the car start! If the previous owner had 4 keys programmed to start the x5 and lost 3 of them, no new keys can be added. I'm sure this is not the case, just food for thought.