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Had my code reader on the car today to check everything was well, noticed something with the alternator and wondered if it's normal or not..
When at idle and under acceleration my voltage reads 12.8-13.0v, and during driving if I come off the throttle the voltage jumps up to 15.0 - 15.1v, is this a normal with the b9 as other cars ive owned have always been a stable 14.6-14.8v regardless of been at idle, under acceleration or coasting.

It's normal. Most modern cars have a "smart alternator" so will not output a constant 14.6V. It is to meet emision standards. Anything with stop/start will have a smart alternator and the B9 certainly does.
The spike to 15V is the alternator being smart and using the overrun to charge the battery and not petrol.

I think the "other cars you've owned" were not built to the latest emision standards, maybe you're thinking of some older cars.

Thanks for the answer. Never noticed it before so it caused a bit of panic.