The fob batteries do last a while, but you don't know how long since it was last changed... I have an 07 G35 that I purchased new and I've changed them maybe 3 times since I got the car. Used to have an EX35 and I think I changed them even less. Indeed, but I remember renting an Altima recently and it looks like someone had super-glued the metal key in place or something, because it wouldn't come loose. Starting the car shouldn't be a problem either though, because there should be a port somewhere near the left side of the steering wheel where you can insert the whole keyfob to start the car, even if the key battery is dead.