I am reviving an old thread as I have exactly the same problem.

Has anyone else had success in charging the XT660ZA battery without moving the tank?

This person seems to (my Danish is not perfect) have accessed the battery by partly removing the tank, but Pleiades statement in this thread seems much more attractive to me. http://www.tenere.dk/forumnew/forum_posts.asp?TID=6488

I am not very close to my bike right now, so I will happily take suggestions. If someone wants to share their results, that’d be great!