I need to replace the battery in my Nightforce ATACR 4-16x42 F1. Unfortunately the side cap will not unscrew and I don’t want to break the stop. I called Nightforce and they said this is a common problem and offered to replace the battery, but I would prefer not to ship the scope back to Nightforce. They suggested pinching the inner barrel while I turned the outer cape counterclockwise, but my fingers are much wider than the narrow band of metal exposed on the inner barrel. Has anyone had this problem and found a solution to removing the battery cover?
Why would you not want to send it back to NF for replacement or repair?
Something like this may be thin enough to grip the inner barrel.
Probably because of the hassle of taking it off of the rifle, mount/rings, finding a box and taking it to fedex then putting it back together and confirming it stayed zeroed.
And paying to ship and insure. And waiting to get it back.
All to replace a $2 battery. 
I hope you get it sorted out OP.
Okay I get that (un-mounting, shipping, re-zero, etc), but if it becomes a recurring problem every time you go to change out a battery then I’d want a permanent fix. Maybe I’m just not understanding the mechanics behind what’s really going on?
I never received any notifications that anyone responded to my question and I thought I would check back. I see there are several responses now and thank you to all that responded.
I did try cutting a thin strip of filament reinforced tape and wrapping it around the inner barrel while I tried to turn the outer cap counterclockwise, but it would not budge.
Recently I thought I would have another go at removing the battery cap, but first I decided to check out the battery cap installation on another Nightforce ATACR scope I purchased earlier this year. It unscrewed easily and I inspected the installation. Next I tried the Nightforce ATACR 4-16x42 F1 and noticed for the first time the index marks for the parallax adjustment were over 180 degrees out of alignment. I obviously have a serious problem and will be contacting Nightforce to return the scope.
That was quick. I shipped it to Nightforce on Thursday and I received it back the following Thursday. They replaced the battery cover and indexed the parallax turret.
Thank you Nightforce !!