2006 S500, where is the battery?

Assuming you didn't drill the lock, it would have been best to access the interior of the vehicle (if not deadlocked, breaking in would be relatively simple) and current could be supplied to the vehicle via the cigar lighter or from under the hood by connecting to the battery circuit in order to use the in-car trunk release if fitted.
A way into the trunk can usually be found by removing the rear seat or hooking the keys using a fishing tool through the armrest aperture if there is one.

The underhood connections can work by themselves...POS to POS, and NEG to NEG...sometimes dirty/weak connections do not allow the power to transfer fully from the underhood connections...if this is the case then you need to connect directly to the battery in trunk for full power charge...again POS to POS, and NEG to NEG...hope this helps

Sigh. Okay, what have you tried in the way of fixing it? Have you just gazed at it and hoped that someone on this forum will drive out and do the repair? Did you:
- check if the bulb is burned out, duh?
- see if there is 12 Volts going to aforementioned bulb?
- if 12 Volts present, is ground okay? (and I don't mean terra firma)

I had this problem also, does your third brake light come on? Also is your trunk light functional? If not there is a rubber boot from the car to the trunk lid, that those wires
run through make sure that the wires arent broken in there. That rubber boot on
my 06' Charger over time curled towards the window and got pinched and severed
all the wires. I soldered them and replaced the blown fuses in the trunk fuse box.
Problem solved.

You can buy a cheap battery charger that plugs into the lighter socket that will allow you to charge the battery enough to operate the trunk release.

Hi, if you can open the hood, use jumper cables to open the trunk. Connect the negative cable to chassis ground or even the engine. Connect the positive cable to either the big nut on the starter solenoid, the fuse box, or the big charge wire nut on the back of the alternator.

Enter into the trunk space after folding the rear seatbacks down. Pull the yellow emergency trunk release handle that should be dangling right beside the area where the trunk latches to the car. This should get the trunk open so that you can expect the locking mechanics for damage: bent steel, something foreign stuck inside, bad cable, etc.

Trunk< under left panel>

There are unit that you can get from the Auto stores that allows you to plug into your cigarette lighter that should supply you with enough voltage to open your trunk.

Look under your hood, you will find contact points for jump starting. If you have a battery charger, you can connect it to those jumper points, and that will give you enough juice to operate the trunk lock.