My 2003 SL500 door and trunk locks do not work with the smart key and I must use the mechanical key to unlock them. The smart key battery appears to be fine since the the light on the smart key remote lights up when the lock/unlock buttons are pushed on it and the sideview mirror lights up as well. However, the locks only work with the mechanical key. The switch inside the car for unlocking the trunk also does not unlock the trunk. What is the probable cause of this problem? Can it be the electrical consumer battery or fuse? What's the cost for a new battery?