Didn't I say that earlier?
Yes, you did. I'm with you.
72Ah are very different from 70Ah - the differences in the 'Cold Cranking Amps' (CCA) is very noticeable.
And many TDIs have 80Ah batts. .
Possibly.
AGMs are still very expensive - a quality calcium or calcium/silver battery with a healthy-sized CCA is probably more than adequate for curing sluggish cranking.
Many cars come with AGMs from factory, eg all Audi TT (sic), all BMW 1 series, most BMW 3 series . . .
They are used when the battery is not placed in the engine bay.
These are only 20,-- - 30,-- pounds more than a conventinal battery. Of course there are more
expensive racing types (which are small but strong) and the lead/calscium VW uses in the Golf
are pretty good as well.
And yes, don't listen radio without engine running - at least not in the winter !!