[savs]

Will the key not open the door? The mechanical key inside the key fob. Should open the door mechanically and let you in. Then go through car to the back.

 

[savs]

In an A5 the split seat will drop from cabin (no need to open boot).
Lifting boot cover (if battery in spare wheel well) might be awkward from that angle. But all modern cars have mechanical boot releases from inside car (not sure where on A5 though)