Hello and welcome to JustAnswer!
If the battery is good then most likely the problem is with the transmitter itself and the key will need to be replaced. The first thing that should be done is test to see if it is sending a signal when pressing a button. Any dealer and many shops will have a radio frequency tester that will test signal strength. Many parts stores here in the US also have these testers and will test key fobs for free, this may be something that is also available in your area.
I have tried the spare key but the same problem so doubt that both transmitters will be faulty. I unlocked the vehicle and literally 2 min later when I wanted to lock the vehicle it was dead. Also the Central locking ofcourse is not working either but works with the key manually. The red LED on the dash- also is not flashing anymore when the vehicle is locked. I have checked all the fuses etc.