What is the volt Meter in my Cayenne Telling Me

[majordad]

How does the Volt meter work and what is it telling me ? It reads 14V at the moment when driving, is that good or bad ? The battery went flat recently , I hope due to the very cold weather and being idle for over two weeks and not being driven much begore that but I'm a bit worried. If the battery is Kaput what reading would I see. There is no reading at all when you just insert the key, it needs to be running to get a reading.