This is my ideal light: https://www.fenix-store.com/product_info.php?cPath=22_50&products_id=403
It runs on one lithium or one NiMh AA cell.
However, to make it perfect it needs a way to:
1. make into a headlamp
2. put it on my bike handlebars (NOT on my head). I love the strobe feature for the bike. This allows two markets to be tapped.

It requires only 1AA.
If it requires 3 AAA’s I immediately look elsewhere since 1AA is lighter and much cheaper to run than 3AAA lights. And it’s easier to charge one battery vs 3 AND it’s easier to buy in 1’s than in 3’s

Other things I look for:
1. It must turn on at 0F.
2. Waterproof
3. Easy battery change (that knocks out most headlamps)
4. Long runtimes on one AA.
5. Output stays flat as battery dies.

-Barry