Your Bosch dynamo has an output of 300 watts at 12 volts’. The standard regulator is rated at 25amps. So I guess the 22amp option that you are looking at would be fine. After all, you aren’t using the full capacity of your dynamo which was intended to run electrical extras as used by the police. Unless of course, someone better qualified knows differently. I’m always happy to learn.
Had a splendiforous ride out on early Saturday evening along the Essex/Suffolk borders, then staying over with some pals in Manningtree. Sunday morning the old Jug starter seemed a little slower than usual - maybe that battery is feeling the pressure now. I might swap in the one from Blue for the rest of the summer.
But best I test the VR at the same time - I don’t want to end up with a bill for two batteries. Is it just a case of checking I’m not getting any more than around 14.5 volts with a few revs dialed in?