Coincidence that this thread got revived.
I've been playing around with designs for the circuitry to make a red dot.
Even with a 1mA draw LED, a big CR123 battery with 1500mAh is looking very simplistically at a max of 1500 hours run time.
3000 hours with very low draw 0.5mA.
The Primary Arms 50,000hr thing is working with a CR2032 hovering around only 200mAh o.O
Crudely, that's a 0.004mA draw. I don't know of LEDs that work with that, for constant on, anyway.

Then you get into methods of stretching runtime like not actually having the LED constantly be on, but actually pulsing it at a frequency above the threshold of human perception. For example, a light flashing at even just 60hz can appear to always be on, but in terms of stretching runtime, maybe you can double it by flashing it so it is imperceptibly actually off half of the time that you think it's on.

There are some simple circuitry tricks to eke out juice from batteries, but at its core, red dots are extremely simple. I've yet to figure out the kind of LED they're using, what they draw, and if they are using the pulsing trick and additional joule thief type circuitry to get more out of the battery. I will probably sacrifice a few red dots to see all of the components myself.