I was curious how long a PA Micro would run on a setting that I considered useful for most any situation I would use it in so I decided to turn one on and see. I used a new Gen 2 Micro with the factory battery that I set to setting 5. I did not check it every hour so these numbers are + or -. On setting 5 the dot remained at the same intensity for approximately 220 hours. I compared it to an identical micro that I only turned on to compare the two optics, then turned it of till the next check. After 220 hours the dot faded to approximately setting 3 and continued to fade to setting 1 intensity. The dot finally dropped below this level after 192 additional hours. This is not a scientific test, but it does give you some idea of how long one of these will last when left on.