My fat battery is a 70 Ah type as well while I know A3 2.0 TFSIs just having 60 Ah.
Keep in mind ''Amp hours'' isn't the one and only. ''Cranking Amps'' is even more
important ro start an engine.
So if you don't listen to music while the engine isn't running I don't see any issue
reducing the Amp Hours radically.