it's easy to stitch the pieces together - there are several ways to do it. If you don't want to do that, there are usually sewing groups in the community that will take batting to use in their projects.
As quiltinghere said, they can be zigzagged together ( slightly overlap the pieces then use the rotary cutter to cut thru the space there the batting is doubled - this creates perfectly aligned edges - throw away the small edges and use a wide zigzag or wide multistitch zigzag to connect the two....there is also an iron-on tape you can now purchase just for connecting two pieces of batting, and there are other techniques that folks use.