I'm with Lori on this. Wash them!! While true batiks have been in really hot water to remove the wax, there is usually still dyes floating around.
Batiks work great for tops, but some batiks can cause problems as backs. The weave is so tight that the needle tends to break threads instead of going between the threads. Sew Batik makes their wide backs from goods that are like quality quilting fabrics, and use the batik techniques for the color. I use them for my own batik quilts as well as recommend them to my customers because they are a well made product.