Thanks, Haertig. That's something so basic to me now that it totally slipped my mind. Yes, these different batteries may all have basically the same form factor, but they have different characteristics, most importantly for most users, voltage.

Fortunately, as lithium ion batteries have become more common--at least among flashlight hobbyists and certain power users--more and more LED lights designed for one or two CR123 cells are capable of also using either primaries or rechargabeables. It's critical to double-check that before use.

It really sucks to unwrap that cool DX light that you've waited two months to be shipped from China, and then you fry it because you put lithium ions in the light when it couldn't handle the extra voltage. Then all you have a cool looking paperweight.