Here's a general rule of thumb: for the highest output for a given power for a halogen incandescent the rated life of the lamp is on the order of 10-30 hours, and just off that peak the lifetime jumps to 50+ hours. Sacrifice just a little more lumens/watt and you can get hundreds and even thousands of hours.
While the first part *might* be true, the second definitely is not.
Bulbs die because the filament evaporates. Bulb lifetime is *not* how long until it burns out, it's 'how long it takes XX% of the mass of the filament to evaporate'. You can sometimes see this inside old clear bulbs as dark or shiny deposits, more often near the base (and therefore the source, the hot filament). This is, in fact, one of the reasons normal bulbs are frosted. So the standard doesn't involve dead bulbs, but live ones run for a while until the average filament looses the 'fatal' mass. In general, the hotter the filament, the faster the evaporation, the shorter the life.
Now comes halogens to change the rules. This is a special gas, not a vacuum. This means more heat loss, so right off we need more power, lumens/watt goes down. But if we go higher still, as the temperature goes up (and with it light output) the temperature of the gas goes up with it. Evaporation is going up as well, of course. However the *hot* gas has the ability to cause a chemical reaction that can reattach the Tungsten gas atom *back on the hot filament*, rather than letting it condense out on the colder surfaces. Neat part is where the filament is hottest (it's weakest point) this action is highest, to a first order it becomes self healing.
Under drive a halogen and you revert to 'normal' lifetimes for incandescent bulbs (even lower, actually), and the efficiency (in lumens/watt) goes way down, much lower than 'standard' bulbs at the same levels. At these levels, these bulbs are clear losers.
The 'magic' chemical reaction no longer happens.
Likewise, running batteries flat on such bulbs is probably a bad idea WRT bulb life. While I can't cite such data, I bet that you can kill one faster by under driving it the 'right' amount. For sure doing so, takes lots of useful lifetime off the bulb.
Doug Owen