No, this is normal. From time to time wayward drops of juice will seep off the coils inside the tank and gravity will pull it down toward the battery connection.
Additionally, this situation happens with all tanks that have a metal center tube. The larger the center tube, the more noticeable this is. The center tube is cooler than the vapor traveling through it. This causes condensation to form and gravity pulls that down toward the battery too. This will be more noticeable if the tank is cold (air conditioned environment, outside during the winter, etc).
To insure the best connection with the battery, you can clean the threads with cotton swab, tissue, or the Johnson Creek Cleaning Cloth.