Wrap ShowCtrl in div
Add checkbox to batch details table and keep current selected batch detail ids in $scope.selected
Add $scope.selectedURLFormat which contains all batch detail ids URL-encoded
Add link to /batches/download_xlsx/… to batches#show view
Add route batches/download_xlsx
Remove unnecessary semicolon
Add axlsx gem
Add zip/zip gem for axlsx

Otherwise axlsx won’t be able to load zip/zip, see https://github.com/randym/axlsx/issues/234.
Implement batches#download_xlsx
Make download_xlsx relative and an actual HTML5 download link
Generate download url using url_for and add &ext=.xlsx
Only show download link if any batch details are selected
Make AngularJS work with Turbolinks

See http://stackoverflow.com/a/15488920.