The battery search is over - the original battery died this morning. Over the past three days the car would start, however the dash voltage meter would then drop to below the quarter mark, and then would take about a minute to stabilise in the middle. So I knew the end was imminent.
Had to call ADAC (I have their ADAC-Plus European recovery membership, only €79 a year), the AA van arrived 45 minutes later to start the engine. Then picked up a £72 Exide battery (720 CCA, 4 year warranty) earlier today from Euro Car Parts - they also sell them online for £82 including "free" delivery.
Thanks for all suggestions, they were very helpful.
