Can you calculate how long it would take to drain a battery given the watts?
Considerations: Your LED runs at 3.3v.


mAh how much energy you have on your battery;
Know how much you'll be using every hour;
Consider that an amperage is a coulomb per second;


The Math: Calculate how long the battery will last by dividing its total charge in mAh by your LED load in mA.

900 mAh / 666mA = 1,36h
(I've considered your LED is 3.3V meaning 2,2/3,3 = 666mA).

If you're unsure about my math, you can also use this online calculator that will give your the same result: http://ncalculators.com/electrical/battery-life-calculator.htm