Lamps with a "standlight" facility give sufficient output at junctions. Rigging an auxilliary battery is really not required these days. Have a look at Harris Cyclery or Peter White cycles for some examples.

I live in a really hilly town, so use a generator headlamp, but power it with a 6v lead-acid battery instead of the generator*. The beam pattern is much more efficient than sealed units. It is designed for road cycling and gives a very concentrated rectangle with a set of peripheral spots. The off-road lamps tend to be more even in their distribution.

My touring bike has a Nordlight powering a Soubitez lamp, which really pumps out the illumination. Ive used it in pitch black country lanes at night. The rear lamp of the ESGE fenders is also much brighter than any LED. blinker.

If I was buying a generator today it would be the Lightspin, no question about it.

My LBS can braze mounting tabs for about £15. I dont think you can do this on Al frames.

* Its a home made system, just a stock 6v cell stuffed into an old waterbottle, but with a constant voltage charger. You can fit any cell or lamp you like, 6v or 12v.