Don't mind us. We like to discuss questions like this, but we take them quite literally. When you ask for the longest running flashlight below 100 lumens, someone will dig up a flashlight that outputs way less than 1 lumen, and which runs on a 14000mAh power bank. It might run continuously for a over a year!
So even though you asked for the longest running light, my reading is you don't mean that literally. You're just trying to find out what lights are available from the major brand that have good runtimes. I don't think you are interested (yet!) in the expensive custom/modded flashlights that are also discussed here.
The most important factor will be battery type. For batteries that are commonly used in flashlights, Li-ion rechargeable batteries probably have the highest capacity. 26650 and 18650 batteries are the ones you see most often. A typical 18650 battery stores the same amount of energy as three or four AA batteries. 26650 stores even more.
Li-ion batteries are used daily by hundreds of millions of people in mobile phones and laptop computers. In normal usage, they are quite safe. Li-ion batteries can be finicky, however, so you have to commit to learning how to take care of them. With Li-ion, you want to buy only high-quality batteries and chargers. Rarely, and usually only after abuse, they can vent with flames. In my opinion, you should stay away from brands with names that end in xxxx-Fire. There are a lot of fakes out there, and some of them are dangerous.
The rechargeable alternative is NiMH batteries. The brand I like best is Eneloop. Those, of course, also require a charger.
There are also non-rechargeable, "primary" batteries. These come in two flavors: alkaline and lithium (which is not the same as Li-ion).
So, your first choice is what type of battery to use. Right on the heels of that, you must decide how many batteries you want your flashlight to use. Obviously, two batteries will give you longer runtimes that one. Four, more than two.
The next choice you face is whether to buy a flashlight can throw its beam a long distance or to buy a more general flashlight that provides somewhat less throw, but which has a broader, floodier beam. The fact that you did not mention this make me think you want a general purpose flashlight that combines a bit of throw and flood.
Budget, which perhaps should have been mentioned first, will be another important question.
