Hot to figure out the draw from leds.?

Here is what I have going on in my mind. I have a cabin in the woods that my friends and I stay at. It has no running water or electricity. I Have a large supply of LED's that I just bought. The specs that I have received on them are as followed.((( Emitted Colour : White, Size: 5mm, Lens Color : Water Clear, Forward Voltage (V) : 3.2-3.4V, Current: 20MA, Luminous Intensity: 1300~1500mcd. What I am trying to figure out is how many LED's i can use to run off of a 12 Volt car batt aprox 500 cranking amps. I need the light to run for about 8 hours before needing recharged. I have a Solar 12V charger to charge it during the day. The light will be used at night so it will have to run completely off of the battery. Also i would like the Formula that you used so that I can figure out more lights on my own. Thanks For the help,ya'll.