Opening the trunk without the master security key

Check your owners manual, there is usually a manual cable inside of the vehicle to release the trunk for just such an instance.

Open the door and remove the fuse box cover at the bottem of the A post. You might have to remove more of the plastic trim and take a positive lead from a battery to the red stud and take the black earth to the body this will power the boot.

Unlock door with valet key to shut alarm off and remove the trunk release switch. Jump the trunk switch wires together for a second and it will open

1. Open trunk
2. Place latch in lock position
3. Pull inside trunk release to see what isn't moving
4. If trunk key won't turn, the key may be worn out and need to be replaced

You should be able to pull down your back seat and pull the safety pull inside the trunk.

I vaguely recall reading something in the owners manual of my '97 328 regarding the trunk and the master key. Something about locking things with the master key so that valets cannot open your trunk with the valet key.
Try unlocking the driver door or the trunk with the master key (the original key that had the LED flashlight in it.

you can charge the battery from the engine compartment. check your owners manual that is the correct place to jump and to charge the battery.

I have the same issue (battery is completely dead in my 1998 Mercedes C280 and I can't pop open the trunk). I looked under the hood and have no idea where the positive charging post would be - can anyone help me find it? Thanks

cover under bonnet with a big P on it and negative is anything metal on the engine

2000 jag trunk locked dead battery-use MASTER KEY ONLY to open trunk location is above rear lic plate looks like hex screw ---the valet key will not open trunk-you cannot go thru back seat thr release for them are in the trunk-hope this helps someone