The battery inside of a Nissan vehicle key fob is a small, round, 1.5-volt battery. The electric key has three parts to it: the lower and two upper pieces. The key is held together by pressure. If the battery is dead, then the keyless entry and/or wireless start will not work. You will need one basic household tool to disassemble the key fob.
Place the edge of the screwdriver between the crack where the upper and lower pieces meet. Turn the screwdriver in either direction until the pieces separate.
Pull the key fob apart and set the pieces onto a table. Pull the battery from between the two upper pieces.
Insert the new battery between the two upper pieces. Make sure the battery is in the same position as the old one.
Reassemble the key by putting the pieces back together and applying pressure until it snaps back. Program the key according to the owner's manual.
Your owner's manual will contain instructions on reprogramming the key fob.