Just a note on the Altiods/Sucrets/DIY versions. If you use two 9 volt batteries, run them in parallel to keep voltage ~9. In series, you will be giving your regulator 18v and making it drop 13v to get your 5v out! Most of your battery juice would then end up as heat emanating from the regulator.
Also, and I forget where I read this so judge my credibility accordingly, the fixed regulator IC's like 7805 and 7812 are supposedly much noisier than the adjustable ones like LM317. Power supply noise can be a big deal (and probably accounts for a lot of the MT's own noise). Possibly not in this case though, as it's an external supply and battery only (hence no AC or rectification etc.), but just something to be aware of. LM317 is a bit harder to implement as well, requiring an extra resistor and fiddling to get your exact output voltage.
G'night!
Sanaka