2002 S500 - can't gain entry into the trunk. The battery was disconnected for service and the trunk deck lid subsequently closed (but not locked). Now, the trunk won't open when the release button is depressed not does it respond to a mechanical key.

All four doors are presently unlocked and the hood can be opened... but the trunk can't be opened with the mechanical key... it was recently renewed by the dealer; the lock function (when the key is turned to the right) feels normal but the unlock function (key turned to the left) doesn't feel correct, as if too little resistance.

This model year doesn't have the (+) post in the engine compartment. Any other accessible location where a battery could be introduced to power up the central locking system and the remote key used to open the deck lid?

If not, any other suggestions?