The 2006 Nissan Murano is available with either a standard key or an intelligent key. The intelligent key allows you to start the vehicle's engine without inserting the key into the ignition. This key uses the "Engine Start" button. The intelligent key is powered by a small lithium battery. Every 18 months or so, you'll need to replace the battery. You can do this on your own.
Turn the intelligent key over so you are looking at its backside. Push the small tab upward and hold it in position. With your other hand, grasp the top edge of the intelligent key and pull outward. The backup mechanical key will slide out of the intelligent key.
Inspect the the top edge of the intelligent key where the backup mechanical key came out. You'll see a small slot about a 1/4 inch wide. Wrap the tip of a flat head screwdriver with a soft cloth. Insert the tip into the small slot on the intelligent key. Turn the screwdriver to the right or the left. This breaks apart the two halves of the intelligent key and opens the case. You'll see the intelligent key's battery inside.
Lift the battery out of its holder. Insert your replacement battery into the holder. Verify that the "Positive" symbol on the replacement battery faces upward.
Align the two halves of the intelligent key. Squeeze them together to snap the intelligent key back together.
Insert the backup mechanical key into its slot on the top edge of the intelligent key. Push it down firmly to lock it into place.
