Worthless vehicle warranty when it comes to replacing the vehicle battery

Have a motor plan for the VW Taureg i own which expired in December 2022. In November 2022 i noticed my car battery was not reacting as it used to so took it to my service dealer in Somerset West. They wanted to keep the car for 3 days for tests and the feedback after this was that the battery was fine. Mid Febraury 2023 my battery needs to be replaced. Now i ask myself how with all the world class diagnostics this can be possible. Surely the tests should have picked up something if 3 months after these test i have total failure of the car battery. The service manager at the dealer said it was almost impossible to get a battery replaced under warranty so i referred the matter directly to VW South Africa. They came back yesterday stating that they have reviewed the test results from November and that they are unable to assist as the test results showed that the battery was in working order. How is this possible !!!! Surely the results should have revealed that at certain times the battery struggles to start the vehicle which is why i took it in in the first place. I cannot believe that between November and February i now have total battery failure and had to pay for a new battery???