Bootstrap 3 uses panels instead of the accordion class. The template should change for that. Not to change ui-bootstrap, I overwrote the module that has the template for the accordion. This module should be added to your js class (and should load after ui-bootstrap):
angular.module("template/accordion/accordion-group.html", []).run(["$templateCache", function($templateCache) {
$templateCache.put("template/accordion/accordion-group.html",
"<div class=\"panel panel-default\">\n" +
" <div class=\"panel-heading\" >\n" +
" <h4 class=\"panel-title\"><a data-toggle=\"collapse\" ng-click=\"isOpen = !isOpen\" accordion-transclude=\"heading\">{{heading}}</a></h4>\n" +
" </div>\n" +
" <div class=\"panel-collapse\" ng-hide=\"!isOpen\">\n" +
" <div class=\"panel-body\" ng-transclude></div> </div>\n" +
"</div>");
}]);
angular.module("template/accordion/accordion.html", []).run(["$templateCache", function($templateCache) {
$templateCache.put("template/accordion/accordion.html",
"<div class=\"panel-group\" ng-transclude></div>");
}]);
Find this sample in plunk