Not having a user replaceable battery generally means you can not order an original Apple replacement part in an Apple Store or on the Online Apple Store. The battery will have to be replaced in an Apple Retail Store through the Genius Bar or by an Apple Authorized Service Provider (more info). Ordering a non-Apple battery and replacing it yourself or having a non-Apple Authorized Service Provider replace it usually voids your warranty. More Info on battery replacement here. MacBook Pro specific information here.