My remote initially ate through batteries very quickly, probably because I put them in my bag where some object in there would press one of the buttons until the battery ran out. I've since alleviated this by putting it in an unused spectacle case so nothing would be pressing any buttons thus draining the battery. Problem solved.
To determine whether it's working, fire up Photobooth and point the remote at the camera. If you see no white blinky light, you're battery is dead. Go to Kmart (or whatever the UK equivalent is, since there sure are a lot of Brits on this board ;D ) and get yourself a new CR2302. If you see a white blinky light, you still have power. If you see a dim white blinky light, it's probably not enough to trip the sensor. CR2302.