A remark on voltage regulators. The standard linear regulators will get hot if there's a lot of voltage getting stripped off (essentially the difference in voltage is lost as heat, which will drain batteries much faster), which is why they come with big heat sinks. You still need to keep the heat sink cool, though. That's all in the datasheets. Switching regulators or dc-dc converters don't have this problem, but they can be tricky to integrate. I've used a switching regulator that has the pin out and rough form factor (it's a bit bulky) of a standard 78xx linear regulator. They aren't cheap, but aren't that expensive either, and make life a lot easier in some cases.
http://www.recom-international.com/prod ... -hole.htmlhttp://search.digikey.com/us/en/product ... ND/2256215
