I'd have to go back to a previous thread with Gary that we had earlier, but LEDs behave a bit differently than incandescents. Let's unravel this a bit...these lamps are rated at 3 watts. Watts in DC are volts x amps, so if your voltage is 3 C Cells x 1.5v = 4.5v...then 3 watts divided by 4.5v = 0.67A, or about 700mA (I think I measured 550mA, but no matter...close enough). So if you had 3 cells in series at 9000mAH (can produce 9A for 1 hour) capacity, because they are in series, you have 9000mAH divided by 700mA or potentially 13 hours of run time.
Nuff said. I lost everybody, I know, but that's how it works. Raise the voltage, lower the current, lower the voltage, raise the current. Watts is watts.