The battery will go in the stock location, inside the upper, above the gearbox. Once I modify the bolt slide/cover, up to ten mini cells will fit. The black gun at the start of the post had a 12v battery inside.
I build Replicas of Antique Browning 1917's, 1919's, and M2's for a living. When I build a "fantasy" gun, it's just to shed some "historic accuracy" usually. Please, just ignore my posts, you know they aren't for you now.
Just like there's a lesson in every failure, there may be some technique or method shown here that might make a more "sane" project easier for somebody.
While painting the uppers for the SCAR, I left some paint stripper a few minutes too long, and...disaster...how many folks have done this? The plastic was all softened, coming off with the paint in goopy hunks...what to do?
Wait till you see...and be sure some people will ask "WHY?"...