I'm trying to use AngularJS Batarang when lean to build a MEANJS App.
Here is the tutorial URL: http://www.bossable.com/656/mean-stack-mongodb-angular-scope/
What I find is my "Scopes" tab's presentation is different from the tutorial video and has an error printed.
My result of Batarang Plugin.

A result from the tutorial.

I don't know if it's because the different version of Batarang, or the error printed.
Your error "Uncaught TypeError: Cannot read property 'getToggleElement' of null)" is not related to Batarang, it's actually from angular-ui. It appears when you select an option from a picklist. I believe it has been fixed in the most recent version.
Here are some quick steps to show you how to remove your existing version of AngularJS Batarang, and how to install a ‘working’ version.
Checkout the video here: http://www.bossable.com/1157/angularjs-batarang-in-chrome/