No need for an agm, the car might not even coded to take agm batteries. Registering the battery will not change that
From the top of my head the car can't even be coded for 95ah agm.
E60 m5 should be in 100-110ah, ideally 110. Do not compromise on the battery quality. I use to sell the Varta 110 for m5/535d etc but I am out of stock.

720amps you had before is a joke.