The battery is dead and the car booth would not open to reach the battery?

Can you open the hood? If you can get the hood opened, there should be a positive battery terminal meant for jump starting on or near the intake manifold.

Thanks for that,yes I can get under the hood. Charged the battery for two days,still would not start?! As I mention I am aware of the system shutting down,managed today to get to the boot,and eventually to the battery. Followed procedure of disconnecting the battery, waiting and turning the key after 10 minutes. Something I,v done before in the similar situation,and it worked in the past,but not this time though. I noticed something strange was happening,while charging,apart from alarm beeping the left light,on the side of the terminal, was flashing all the time?! I refrained from the jump start knowing how damaged to this car it could be,and to be honest I don't think it would work taking into account the shutdown of the system. Do you have any further ideas?

Ah, okay. I thought you meant there was no power to open the trunk to access the battery. Obviously, you've discovered that the car is in it's immobilized state. I'm not an expert on the alarm system, but I can direct you to bimmerfest.com. Search "X5 EWS." EWS is BMW's immobilizer system, and it seems lots of people have had issues with it after the battery dying.