Ever since we fried a D-link in my first year as a Mentor, all the dlink/camera connections are tested for polarity and voltage before first use.
Similarly, a few years ago, our team acquired a Battery Beak to test batteries before use. It has the added feature of testing for polarity. When a battery is first wired, we use the Battery Beak to test for correct polarity.
http://www.andymark.com/product-p/am-0995.htm