Figuring out the terminals on the battery

One problem that we were having was trying to figure out which terminal was which on the battery in terms of negative and positive. I wanted to hook up a LED to the battery because LEDs will only light up when hooked up one way. The problem was that we only had 5v LEDs which wont work with 12v without blowing them. I asked professor Sullivan and he said that I should take advantage of the voltage drop that happens with each LED when they are hooked up in series. Each LED has a 1.7v drop when hooked up in series so I hooked up 7 LEDs with a resistor just to be safe. The circuit that was made helped to figure out the battery terminals. You can see in the pictures below the circuit only lights up when hooked up one way.

-WK