Dead battery so trunk won't open - 2002 Volvo S60

Here is the link to the owner's manual on the process of unlocking the trunk with a dead battery or dead remote.

The key lock is under a rubber plug to the left of the license plate light.

http://new.volvocars.com/ownersdocs/2005/2005_s60/05s60_07.htm#pg77

You should have a trunk lock cylinder in the trunk lid. Look to the right side of the license l plate by the license plate light and you will see a black plastic cover. Remove the cover to expose the lock cylinder then use your key.