Thanks,
especially to Hector for the calculation. So far was installed a 12V 85 Ah battery under the rear seat, it will now be replaced by a 12V 100Ah.
In addition I have one in the trunk - standard on the Highline because of the cooler box and extra aircon for rear etc.- which is 12 V 30Ah.
So both I have to charge basically to keep them alive.
That is a good hint, that the solar charger does not work so well when installed behind the window glass, like the ones for VW are on offer. So maybe better I get a weatherproof version like this one I found in the U.K. ?
http://cgi.ebay.com/1-8W-Weatherproo...QQcmdZViewItem
If someone knows a source and has a link for a good one, please let me know.
Thanks