PS2 wireless controller problem

[Rocksteadyeddie]

I have a couple of 3rd party (maybe Negcon) controller for my PS2 slim. One connects fine, the other just flashes the red "analogue" light and won't connect. There is no obvious reset button to press. Any ideas what to try, or how to reset the connection? I'm a bit out of my depth with all this gaming stuff!

Thanks in advance