I own two PT headlamps: the Quad and EOS Tactical. Both are regulated circuits that permit a nearly stead light output until very near the batteries' end.
They are great for winter, when lots of light is needed, but too heavy for summer backpacking.
In summer I use a tiny coin cell battery poerered headlamp and carry a few extra of those tiny batteries, though I've never had to change them out until after the end of the season.
Finally Petzl is beginning to sell some headlamps that are regulated AND can accept lithium batteries W/O burning up the circuitry! Personally I much prefer Princeton Tec lights to Petzl. I guess Black Diamond would be my second choice.