I have an old CygoLite Hilux 30 (discontinued) light that runs off a 12v NiCad battery that is now completely knackered. What are my options for a new battery pack? Anyone know how I go about building up my own battery? Will something like this work? Any other ideas welcome.

http://www.batterytastic.co.uk/Search_All.asp?searchall=bottle&Submit4=Go

All help appreciated.

You would need 10 of these wired in series, you can get them cheaper if you dig about.
That pack would work & be lighter than your original although I’m not sure your old charger would work with it.

Nimh/NiCd batteris/chargers often dont play well together. You could stock up on rechargable AA’s and chargers and get some holders from maplins.

10 good quality AA’s would give 12V and about 2900mAh

So does that mean that a NiMh battery won’t work with my Light? Or can I run a NiMh battery at aprox the same voltage?

no as long as it reaches the voltage the lights dont care what kind they are but the CHARGERS are PROBABLY different

If it’s a straight forward halogen light the Enix battery and charger combo you have in the link should be OK. Just sort out the polarity of the lead and socket to suit your light.
You’ll be running your light over volted like many other halogen systems.