rollerce:
I didn't worry about a series resistor for two reasons, the first is that the battery voltage (tested with a multimeter at no load - 3.36V) is substantially less than the LED voltage (~3.8v), so no series resistor is indicated. The second reason was because I was only powering the LED for a moment, not leaving it on for a sustained period of time.Also, this was done after I'd de-soldered the module from the breakout board, because I wanted to test the led without the extra crap on the breakout.
As Mike (more or less) says. Tch tch tch.
Quite obviously the battery voltage was higher than the minimum Vf of the LED, or it wouldn't have lit.
To reiterate what he said: "You must always have some sort of current limiting when using an LED."
(I had to repeat it, that way it will stick in your mind better. 
)