Ah it's just an expression, basically meaning "everything you need included." In the context of web frameworks, "batteries" are typically things like:

- An HTML templating language for your views

- An Object Relationship Mapper ("ORM" - makes talking to databases consistent, and automatically populates your models with data from the database)

- User Authentication/Session Management

- An Admin GUI for managing your database models ("CRUD" Actions - Create, Read, Update, Delete)