Let the discharge leads touch? Yeah, that will make sparks but it's also a very bad thing. You never want to work on more than one battery lead at a time or have more than one battery lead loose and exposed. You'll save yourself a lot of headache if you follow those two rules. There are more but those two are top of the list.
Or sparks when you plugged in the battery? that's normal but you want to try to keep them to a minimum if you can. Try to plug in firmly and not let the Deans chatter around each other. But, a spark in this case is pretty normal so don't worry about it too much.