Get Some F**king Lights

and you will probably need 10bn of them.

a week.
:)

Just out of curiosity what lights use those little disc batteries ?

Not very many of them, tbh. I've got a set of somethings that use disc batteries but the lights were so weak in the first place that rather than replacing the batteries when they ran down I replaced the lights with better ones. I think they're Cateye something-or-others, but really cheapo ones. They're round-shaped with a white plastic surface and a single lonely bulb in the middle, and they attach to headtubes / seatposts using tiny bungee cords.

Edit - these things: http://www.wiggle.co.uk/cateye-sl-ld110-loop-led-safety-front-light/