Ya a battery does fit into that hand guard you'd just have to wire your gun forward. But most M4A1 with a standard CAR-15 (NOT Crane) stock in my research are fore-wired if you have the standard (NO Rails hand guard) begin with. If not It's not a hard thing to do.
*Disclaimer*This is just my experience through about 3 months of research, I may be wrong wait for someone with more experience, This is just what I've read and want to pass on to fellow players.
Originally Posted by FirestormX
I know that isn't really what you asked, but it's the internet, and I like to type things that don't matter.