996 voltage gauge reading too high

[450dream]

I have just put a deposit on a 996 and one of numerous issues that need to be rectified Is the voltage gauge reads to high even without the engine running . To me as it’s still high when not running it’s not an overcharging issue can this gauge be recalibrated or is it a cluster change or repair if possible
I take it that the cluster checks battery voltage rather than getting it from a sensor anywhere?
Any help would be appreciated

[churchie2856]

What voltage does it read?

[450dream]

About 14/15 volts on battery and then near top of gauge when running

[450dream]

I need to verify readings with a multimeter when I pick car up to ensure not overcharging and going to damage something on way home
But any ideas or help will be great fully received