Although my flashlights are standardized on AA batteries, my headlamps are AAA batteries.

The great battery life on these is such that carrying a few extra AAA batteries makes up for slightly less weight and bulk of a 4xAA headlamp. To explain further. Most of the newer AA model headlamps, the battery pack typically sits on the back of the lamp head strap whereas the 3 AAA models, the batteries are enclosed within the light assembly itself.

There are also many headlamps that have Li-polymer or Lithium-ion however many of these have USB or proprietary chargers which presents compatibility problems when the batteries or chargers go south.

Whichever headlamp you purchase, make sure it has a pivoting light head which is very useful as compared to fixed mounted lights.