1. Yes you can
2.
Here is the data sheet
http://www.cree.com/products/pdf/XLamp7090XR-E.pdf
If you are driving them direct each LED will get
From the chart on page 7, 3.3 V is roughly 400 mA
So, to calculate runtime:
Code:
T.runtime= 4500 mAh / 400 mA = 11.25 hrs
This is rough, best case scenario estimate. Actual runtime will be a bit lower and the brightness will be a lot dimmer at the end
3.
To stepdown voltage you would need one of two things
a. Cheapest is to get some resistors. See
http://led.linear1.org/led.wiz
Unfortunately, the LED will not be regulated and depending on setup will waste a LOT of power as heat.
or
b. Best is to get a buckpuck current regulator (this circuit will regulate amperage and stepDOWN the voltage), but it is more expensive.
http://www.ledsupply.com/wired-buckpuck.php
Advantage is about 90% efficiency (again at best) and constant brightness.
I am building similar setup (3x Q5) with 14.4V 1200mAh battery using
http://www.ledsupply.com/03023-d-e-1000p.php
you may not need external pot (to dim/brighten LED), but i chose to have this option.