First some brief background info:

Previously I had purchased an MR16 halogen lamp and some PVC pipe adapter pieces.
I modified the tubing to have a beveled surface and silicon sealed an MR16 into it (replacing a bulb involves removing sealant and gluing in another. Not too big of a deal).
The bulb part friction fits to a threaded piece that screws onto the mount already attached to the front of the bicycle - so the main light portion screws off for maintainability but seals on otherwise.

So, I've got a slick light. No power.
I came across an awesome deal where I got 2 batteries and 2 chargers - 6.0v 1000mAh NiCd cartridge batteries for R/C toys. By wiring them in series I can drive the halogen very brightly - I've not made a holster for it yet so testing involved pressing wires by hand - hard to hold for a long period of time.

Here's my questions:

Has anyone tried this?
Would I get a longer run time if I used two sets of batteries, running them like packs of 12v in parallel?
(ie. 2x6.0v in series, treated like a single battery)

I don't know my run time yet for the reasons mentioned above, but was wondering if anyone else has tried this.