A little digging reveals the answer, Mr Battistelli's position in St-Germain-en-Laye would indeed appear to qualify as "political office". Indeed, the (opposition) socialist party wrote a blog post discussing Mr Battistelli (http://pssaintgermain.fr/office-europeen-des-brevets-laffrontement-social-tourne-au-drame/), describing him as "conseiller municipal de la liste de droite majoritaire au conseil municipal de Saint-Germain".
Thus, it is pretty clear that Mr Battistelli holds office in St-Germain-en-Laye due to standing as an official candidate of the UMP party (Sarkozy's bunch).
But the line-crossing does not stop there.
First, there are unconfirmed (and unconfirmable) rumours that Mr Battistelli's place of employment is not Munich but in fact St-Germain:
Without the details of his contract of employment being made public, we will never know whether there is any truth behind this rumour. However, possible advantages for Mr Battistelli would include: retaining his political position by specifying his primary residence as St-Germain; and qualifying for hefty expenses for travel to his day job in Munich. At least an element of truth in the rumour is therefore not beyond the bounds of possibility.
Secondly, there are a number of official engagements that Mr Battistelli has conducted (or has arranged to be conducted) in St-Germain, for example:
2011 trilateral office meeting (https://www.trilateral.net/news/pressrelease20111110.pdf)
2016 EPO-SIPO meeting (https://www.epo.org/news-issues/news/2016/20161005.html)
2018 inventor of the year award (http://www.epo.org/learning-events/european-inventor/event.html)
This presents a clear conflict of interest, in that the result is money from Mr Battistelli's day job being poured into the very district that he represents in his political office.
So the clear answer is yes, there is a scandal here.