Well, it seems rechargeable CR123A-size (16340) Lithium batteries are higher voltage than SureFire (or other) primary (non-rechargeable) batteries, by quite a lot. Plop those bad boys in an old filament-style flashlight and POOF you get less than 100ms of light before burnout. Burned two just to be sure. 1200 mAh @ 3.7V nominal, fully charged at 4.19V. Guess I should have checked here: http://www.powerstream.com/cr123a-tests.htm
Those “3V” Lithium primaries are barely 3V when brand-new under no load. You get 2.5V for a while, 2V most of the time, and dead at 1.6V. V^2/R is a bit different from 4.2^2 and 2.5^2.