We are Amel 54 #162 and my batteries were this summer at the end of there life- 7 years old.
Sonja Kessler at Amel Med. In Hyeres helped me to arrange to new batteries for a good price. So I would recommend sail up the adriatic sea to venice. Montenegro is a Port for you out of Schengen.
For the Winter haul out the boat in Port Napoleon near Marseille and perhaps Service in Hyeres by Amel. I like La Rochelle very much but I would first sail every corner of the Medsea.
All the best for you/family and boat.
Wolfgang Weber SY Elise Amel 54#164 Cartagena Spain on the way to Gibraltar
This is no answer to your question, perhaps you have to test each batterie with the recommended batterytester (SOLAR) by Bill R. But you have to disconnect each battery. So if they are 5-7 years old I would Change next year.