The battery is in the trunk behind the spare tire. I believe you're talking about the fuse box in the engine bay. That thing in front of it is the ECU, the computer that controls the engine. If so equipped, there will also be another computer in front of that, which controls the automatic transmission.
use a 10mm wrench and remove the battery from the trunk compartment, and replace it with the new battery
At the front of the engine compartment on the drivers side
Drivers side on front of engine compartment
On a 2004 Mercury Sable : The battery is in the drivers side of the engine compartment at the front
At the front of the engine compartment on the passenger side
in the trunk on the right side near the spare, if you need to jump start the car, there is a post in the front engine compartment that easily lets you connect your wires to it.
in the left front corner of the engine compartment under a black plastic battery cover
On a 2001 Mercury Sable : The battery is located in the front of the engine compartment , on the drivers side
front left of engine compartment right around the battery.
LH front corner of the engine compartment.
YJ jacks were located in the engine compartment, front of the battery
It's in the engine compartment, drivers side, in front of the battery.