Another alternative : buy a quality optic.
I play a lot of airsoft, and I've never changed my optic's battery. Sure, it was an Aimpoint CompML2, but, yeah, I mean, if it was an NCStar, and you just turned it off, that would work too. EOTech 512s get battery life out the ass, also.
Cool idea, but seems like a lot of work (and a high ugly factor) for something you could prevent with due diligence. That, and CR025 or whateverthef*ck those batteries are are a dime a dozen on eBay.