I like AA for headlamps! I have a couple of somewhat older Fenix headlamps that use a single AA, great light.

1AA is probably the best small headlamp format, though a lot of them are heavier than necessary. I just edited my post above to link a review of the Nitecore I mentioned.

Fenix currently doesn't seem to make any 1AA lights, oh well.

Think everyone should have at least 1 AA light, just because of battery availablity.

Still have the Acebeam H16 mentioned earlier in this thread IIRC.

Though if had to buy another think I'd try a Wurkkos HD12

https://wurkkos.com/products/wurkkos-hd1...ariantsId=12322

The Acebeam looks nice! My main complaint with the HD12 is that it is kind of heavy, 48g without the battery or strap. More like 90g including everything. The Acebeam is lighter, and if you want just a flashlight instead of a headlamp, the Skilhunt E2A is quite light.

For headlamps the Nitecore HA11 (mentioned) and HA15 (not sure what the significant differences are) are the lightest out there. The HD15 is a few grams heavier than the HA11.

Acebeam H40 also looks interesting.

Added: the HD12 claims to have reverse charging (you can transfer juice from the flashlight to your phone). IDK if it has been tested. It's pretty marginal since the 14500 battery is so small, but maybe it could let you make an emergency call if your phone was dead.

Ok, I got a Nitecore NU05v1 kit (light + headband + bike clamp) super cheap on closeout. This light weighs 10.4g if I remember right, another 9g or so for the included headband, but you could instead do a shock cord headband of 3g or so.

Unfortunately, the light didn't work when I got it: the internal lipo battery was dead. The seller offered me a refund or replacement but I figured heck, I wanted to open it up anyway, so I'd see if a DIY fix was feasible. Spoiler: I'd say it's not feasible.

Instead of screws, the light was heat staked and glued together, so I had to pry it apart with a knife. The battery is also glued to a foam pad inside, and it's an obscure size. I need to measure it but by eyeball it's around 27mm * 27mm * 4mm. Maybe I could order a replacement cell from somewhere and reassemble the light, but this is all a pretty big hassle. These lights new are about $20 each and I can't recommend buying one unless you absolutely require the form factor and don't mind throwing it away when the battery craps out.

The larger Nitecore lipo lights aren't as bad. There's a box you can pry open and the parts aren't so packed inside. Here's a youtube about replacing an NU25 battery:

https://www.youtube.com/watch?v=KnSQir2u_nA

Overall though, I wouldn't buy one of those models either. I'd stick with the 14500/AA powered HA11 or HA15. All up (including battery and headband) they're still in the 2 ounce range, which is pretty lightweight by most standards.

Anyway I had been intrigued by the NU05 for a long time and now my curiosity is mostly satisfied. It's a clever design and a technical feat, but the non-serviceability is a big negative.