Should you have issues with the battery going, or for some other reason you need to access the boot without the key, you can use the manual boot release.

If you have a t-bag in your car, you may need to remove it just for more access.
Behind the passenger seat there is a small flap cut in the material of the carpet.

Lift up the flap and locate the looped cable.

Pull this cable, it should move with little force.