abasel:
Just realised that I would probably need to add a resistor for the LED. This will change my current being drawn.
With high power leds, a resistor is not suitable. You need constant current drivers. These driver circuits will consume a little power themselves, but not much. So your calculation is ok.
But I would echo the warnings about power packs purchased on eBay and other sites. I once purchased some 18650 size Li-ion batteries with a quoted capacity of 9,900 mAh. When I measured them, they were 1/20th of that.