to go back to factory settings i thought you just take the batteries out and leave it for a couple of minutes, then put it back together.
Nope, a bit more complicated. From the NovaTac manual, page 10:
Factory-Reset
1. Turn the light on.
2. Unscrew the battery case until the light goes off.
3. Screw the battery case back together; there will be one second of dim light.
4. During the one second of dim light, press and hold the button.
5. You will see five seconds of bright light, 3 seconds of dim light, 2 seconds of bright light, then the light will go out.
6. Release the button when the light goes out.
7. The factory reset is complete.