I want to have a trunk gun.  The AR I chose for this duty will be equipped with a Primary Arms Advanced Micro dot.  I live in Virginia, summer can get very hot and winters can get very cold.  I know that the temperature abuse will not affect the red dot itself, but I'm worried about the battery and storing it in extreme conditions.  I also have a C-More tactical railway red dot and was wondering the same thing with that.  So is it ok to leave my red dots inside vehicle for long term storage?

Heat is a battery killer. It would fare just as well as any flashlight would (which is not very good) in vehicles in high heat (I can put a brand new battery in my Fenix, and that suckers dead by the end of summer).
I think you'll be fine, just plan on changing batteries WAY sooner than you normally would.
IMHO, something w/o battery, such as an Acog, would be a much better choice for that environment.

Now I'm wondering if a destroyed battery can damage the optic itself because it is the power source the red dot is connected to.  Wasn't sure if heat or cold can kill a battery.  I usually don't leave electronics in my vehicle and my car battery has been reliable every season.  But I would still like to see if anyone else hear has done it.

This. Heat and cold both are tough on batteries. This isn't a concern for me as I go through CR123's like they're going out of style, anyway, but to some it may be. A quality optic will be unaffected by being left in your trunk year round.

Just swap the battery every 3 months. I think you'll be okay. 

I ran an E O Tech 512 with Lithium AA batteries for several years and my rifle/optic road in the trunk of my patrol car unless I had a reason to have the rifle close at hand.  I usually brought rifle into the house on my days off but the rest of the time the rifle in it’s soft case stayed in the trunk.  The Patrol car was never in a garage in the midwest climate.  I never encountered battery issues or wandering zero with the E O Tech.   I usually replaced the Lithium batteries once a year and always carried spares.  

I’d bet the majority of my fellow Officers left their rifles in their cars 24/7 365 unless they removed them for specific reasons (vaction, car repair, training).  Several Officers were using Trijicon Tritium/fiber optic reflex sight with 12 MOA triangle.   Only Officers with supplied rifle optics were Tactical or Snipers everyone else bought their own.   The Department issued rifles came with carry handle iron sights and fixed front sight tower (Bushmaster or Armalite) depending on who won the contract.  The department also aquired a few ex military Colt M-16 A-1’s and changed to semi FCG.

Get in the habit of changing all your batteries once a year and/or after any extensive use like a multi day class or field exercise.

We do this with our M4s, which have a claimed 80K battery life.  Batteries are cheap.

We did the same when we ran Eotechs.  Guess what, dead batteries were never an issue.

Same goes for weapon mounted lights.  I've seen 123s with very little use start to die and the light go dim due to environmental conditions.

Heat/Cold kill batteries as much, if not more than, use.

Batteries wouldn't be what concerns me.

I would be worried about glue.  A lot of electro optics have lenses, LED emitters, circuit boards, wiring, seals, buttons, or switches that are glued in place.

I have a laptop that's been in my car the past couple years, and glue is now leaking out of every crack and crevice.  It looks like someone removed the screen and keyboard, poured half a bottle of corn syrup inside, then put it back together.

I have had an AK with a Ultimac rail sitting in my truck for about ten years now. An ancient and beat to shit Aimpoint Comp M4 sits on top of it. I check it every 6 months. Never an issue. I will put Texas summers up against Virginias any time. Buy good shit, check it from time to time, don't worry.

Can't speak to the resilience of the PA red dots, but neither of my Aimpoints (M4s and PRO) has had an issue in the vehicle. I run Energizer Ultimate Lithium AA batteries in the M4s and replace yearly. The lithium are supposed to be far less likely to leak than alkaline.

It will be fine of it is not exposed to direct sunlight. Had rifles with red dots and lithium in my vehicle for decades without issue.

Quality optics (Aimpoint, Trijicon, Leupold, Nightforce, USO, S&B, etc.) shouldn't be a problem.

Cheaper stuff I'd worry about.

Im in NC

mine has been in the truck over a year

took it out 3 weeks ago, all hits w/n 1" at 50 M with MK262

GTG

My aimpoint died from vehicle heat.


Stuck on the top brightness setting.

Well this is a $1500+ Dell Rugged Extreme laptop made for hard use, yet a couple South Carolina summers inside a vehicle made it ooze glue like a jelly donut.

I doubt Aimpoint has access to some top secret super glue that Dell doesn't.

Granted, a rifle zipped up in a bag in the trunk wouldn't reach the same temps as a laptop sitting in direct sunlight, but still, I wouldn't have much confidence in a red dot that has been in my trunk 24/7 for a couple years.  Personally, I'd just go with irons if I couldn't afford an ACOG or similar.  But I would never leave a rifle in my vehicle 24/7 to start with.

This, and we get some pretty cold winters here in Anchorage... heck we have big arguments up here about what lube WONT gel up at -40...

Rifle case in trunk wont exceed 140 F on a 100 F summer day. Exposed to direct sunlight in passenger compartment, 160-170 F is easy to hit. There is a world of difference in 140 and 170 F.