For a MR-16 bulb like that, I think you're better off with an optronics housing. You can get them cheaply on ebay. I'm also partial to the Malibu LV505 outdoor bulb that Home Depot sells, which is a 12v, 25 watt halogen. It fits into housings that are commonly sold as utility lights for trucks and tractors. Something like this: http://www.autobarn.net/rounrub12vtr.html.

I run my lights off of AA batteries -- a pack of 12 of them. I use 2700 mah NiMH ones that I can get on ebay for about $1.50 each. The thing about batteries is that the voltage varies as they discharge. The NiMH start at about 1.2V and drop to 1.0V when discharged. By using 12 batteries my light is slightly overvolted when they are fully charged and still at full voltage when discharged.


Is that geeky enough?