Hopefully, FD's have a data base showing the locations of batteries in all makes and models. My X5's battery is in the trunk, under the floor and a plastic cover. It'd take Sherlock Holms and @tomrayjr 's sawzall, 'cause the trunk is electronically unlocked and we all know what that means - only works when you don't want it to.
Protip:
You can back feed power into your cig lighter to open something like that if the battery is dead. Happened to me once on my Boxster. I took a 15' piece of speaker wire, and ran it to a jumper battery, and held it to the ring and tip of my cig lighter and it was enough juice to pop the frunk & let me properly jump the battery. Maybe it'll help someone some day!