Going on 6 month vacation should i remove battery
 

I am going on a long vacation.
I have given my Audi A6 2.4 2007 model to a friend who will keep it in his garage.
If i remove battery terminal is it safe for car health including battery ?
OR
should I ask him to drive the car after each 7 day period and without removing battery.
If this is the case , how much time should he drive.
He comes to his home each week for one day only.

Suggest the best solution.