Assuming you are not re-screwing into the same holes that were used previously, and assuming that the timber has not been damaged, or deteriorated from prolonged weather exposure, we don't see why the existing battens shouldn't be re-used if they were correctly sized in the first place. But perhaps Timber Queensland would have relevant experience, as we don't have any specific data on this issue. Their website will give you contact details http://www.timberqueensland.com.au/.