My guess would be your batteries too. Ultrafire batteries seem really crappy, big time. Those were the ones tested here, giving out a measly 302mAh @1A, only 10% of claimed capacity, pretty useless. And its big brother test result here, getting only 779mAh @1A despite claiming 3600mAh (around 20% of claimed).
That battery hardly give out anything at 1A, and I'm sure your 5xQ5 flashlight must draw MUCH more than that! I bet its not even the circuit protection, your battery probably simply run out of juice to maintain necessary voltage for HIGH after two minutes.