You can see the partly finished product in action her
You need to purchase this LED controller off of Ebay, they cost a mere 5 dollars
LED Light Strip Controller
They are available for different battery cells, I have 3S batteries, so the link corresponds to my battery type.
LED Strips. They are purchased in different lengths and colours. Note: There are two versions, a non-waterproof and a waterproof version. The waterproof version is a bit harder to work with as i requires that you remove/cut the rubber lining protecting the LED from getting moist. Cut a strip corresponding to the lenth needed. You need to cut it just before the copper pad as you need to solder your 12 volts power here.