Any progress? An old friend who's a farmer emailed in disgust that his "100 lumen 3xAA" headlamp often fails at night while he's out chasing varmints out of his crop. It's partly his fast NiMH charger killing the batteries--but as he needs new batteries and charger, he ought to get a new headlamp.
I've been looking for something for him (he's got slow web access). Something like this --- battery pack -- seems likely.
i'm not sure if you'll get a response considering the age of the thread.
you can buy ready made headlamps for less than the cost of this build. i have a sku 8238 from Manafont; a lot of headlamps sold by budget Chinese retailers are horrible, but that one is actually decent. it uses 3AA, an XRE (not sure if it really is a Q5, but it's bright), and flood to throw optic that works well. plus it has a good tilter, which is often one of the weakest points on a cheap headlamp. the battery cable is a little bit short, but i haven't found any other obvious flaws with it so far. i've used it as a backyard work light the last couple months and it has served me well. it's not waterproof and doesn't approach the overall quality of a Princeton Tec or a Petzl, but it cost me just under $12 so i'm pretty happy with it so far.