I don't like the fit of the battery in the stock either. However, I love the look and feel of the stock. And I can't fully collapse it with the battery in.
I think I may install a full stock on the 416 and use a large battery, paint the 416 stock OD, and install it on my C8. Screw it if it's not 100% accurate to the real C8. I'll still keep the C8 front-wired as it is now with the 9.6V nunchuck in the foregrip. I like it a lot better than the stock TM retractable stock in terms of feel.