I've had my PRO for 5 years or so.  The battery that was in it, had been in there for a couple years, but I don't leave it on 24/7.

I was taking a 2 day Rifle course this weekend.  It was fine all day Saturday, but first thing Sunday morning I had to put it on setting 9 to even see the dot.  On a break, I changed to a fresh battery that I bought earlier this year.  After about 4 hours, I once again had to jack the intensity up to 8 in order to see the dot.

What would cause my AIMPOINT to blow through a fresh battery like that?

Was the new battery reliable? I have been trying to find new batteries but everything I read on em is they are questionable in their charge. I'm still working on the same battery from when I purchased it as well, many years ago, and like you only turn it on to go to the range.

I bought it new earlier this year.  I guess it's possible that it was older, but if the AIMPOINT is capable of running 24/7 for 3 years, how old would a shelved battery have to be to act the same as one that is 3 or 4 years old with intermittent use.

Buy a fresh battery, test it out.

If the condition persists, call Aimpoint.

Shelved where?  In a hot ass car for a year?

Noticed the same thing with my Pro.  Whatever setting AP advertises the life at, 6 or 7 I think, is not very bright and if you go over that setting battery life drops dramatically.

Holosun is my go to now.  AP can keep their overpriced optics.