I usually wash everything as I hate bad surprises. You can swish the batiks in your sink or a basin of hot water with a few drops of detergent. do not wring or twist. Like colors together!
empty the water & rinse with clear water. I then roll the pieces in a towel & apply pressure (OK, I stand on it). I have a large counter, so I lay charm squares out, patting them into place. With strips, I either lay them out the same way, or drape them over the ironing board. I allow them to dry overnight. If you have the counter space, they don't even need to be ironed.