Spotted Gum Decking to clad wall - batten spacing

Hi,

I have a besser block wall (11m long and 1m high) that I'm going to clad with spotted gum decking (86mm x 19mm). I will be screwing the spotted gum decking to battens that i dynabolt to the wall. A builder i know has suggested that my battens should be 450mm apart. This seems overkill to me, what do you think would be an appropriate spacing?

Thanks, any help greatly appreciated.

roice