How to troubleshoot a dead battery on an Audi A2?

I haven't used my Audi A2 for a while and now the battery is completely dead. What could be the cause and how can I troubleshoot it?

First, check to see if any lights or electronic components were left on, draining the battery. If not, it could be a faulty alternator or a parasitic draw on the battery. You can troubleshoot these issues with a multimeter and by checking for any damaged wiring.

Another possible cause of a dead battery could be corrosion on the battery terminals. Make sure to clean them with a mixture of baking soda and water, then rinse with clean water. This can improve the connection and potentially solve the issue.