if the battery terminals were marked with the wrong polartiy, then it is the battery manufacture you need to sue, not the service guys who cannot be expected to check this, as it is a standard no one expects to be violated. Sparks from a newly charged battery are a bad indication and if they hooked it up when they knew it was sparking then yes you do have a case aganist the service guys, but only for continuing to hook it up after they knew it was sparking. by the way, once it sparks off the leads being connected, most likely the damage to the diodes in the alternator has already been done.