I charged both the ‘useless’ starter-box and the battery over night and I was lucky ;-)
‘The car’ started instantly.
Went to my local VW dealer / garage and inquired how much a new vacuum pump for the door locks would cost me (without labour), and was rewarded with an estimate of above 200 bucks. Not good. It’s a friggin’ electrical motor with a bit of mechanics and electronics. I can get a laptop for 200 bucks, which is obviously much more complex.
The 2nd-hand market offers these parts for about 40-70 bucks. I’ll think about that. I certainly won’t buy a new non-safety-relevant pump for a 20 year old car.