Controller inside card VW3A3501 Battery lifetime is 8 years, is there any alarm when to change battery.
There is no function, which give an alarm when the battery is out of order.
It is possible to check by the program if the battery is ok or not. Declare a variable as "RETAIN" and initialize it with a value (the value is saved in the controller inside board after a shutdown).
Check it in your program and if the value is 0 after a shutdown, it means that the battery is dead.