What size battens with insulated plasterboard?

[curium]

Thinking of using insulated plasterboard on the external wall in my shower room which gets quite chilly in winter.

This board is a lot thicker than plain MR plasterboard so was wondering what size battens are normally used to fix it to the wall so I know how much of the room will be taken up in total.

Thanks

 

[foxhole]

Why batten ? Stick straight to wall.