My friend’s roommate’s car battery died last week. Since she rarely drives the car, it was easier (and quicker) to remove it from the car and hook it up to a charger, rather than jump start the car and have her drive it around.
My little Battery Tender Jr. has been charging it for a few days, but it’s only able to output about 750-900 milliamps (( The specs say 750 mA, but it seems to deliver about 900 mA in bulk charging mode. Odd. )), so charging a car battery takes several days.
I also happened to have another “smart” charger that can put out about 1.5 amps, so I brought it over to their house tonight and had my friend connect it. During the process, he managed to accidentally short the negative connector on the quick-disconnect end of the alligator clips (looks like this, but unfused) to the positive battery terminal. Lots of sparks ensued.
Fortunately, he disconnected the alligator clip quickly, so no damage was done, but it was rather fun for a second or two.
After being connected properly, things seem to be working quite well and the battery (should) be ready to go tomorrow afternoon.
Moral of the story: Don’t short car batteries. They can output a massive amount of current.