Product review (5 stars): Excellent value
I'm very happy with this purchase, and may order more.  I received these quite quickly and well-packaged.  I tested them with a low-current 12V "wall wart", and all five work well.  Don't test these at their rated (or unlimited) amperage, like a car battery.  They will self-destruct within seconds if not attached to a good heatsink on the hot side, as they quickly reach the melt point of the solder inside them.  Yes, they get that hot that fast.  Lower current will work more slowly, preventing damage and possibly a painful burn.  A 9V battery would probably work well.
I've read reviews of this part number that said the hot/cold side varied in regards to the printing location, but on all of mine the printed side is cold when the red lead is connected to 12V+.  If you get variances with that, they're not defective! Just use a Sharpie to mark the hot side so you install them correctly for your application.