Well Im just the guy to ask about all this.
I have the Full HK marked VFC HK 416 Super DX, plus about 1,800 USD extra in and on it. I have that exact battery from onlybatterypacks. That battery is IMO the best for that stock, it has such high Mah (4200) that I have only charged it 3 times since September. About the connector back when I orderd it came with a large connector I guess they chanded it to the small tamiya now. Either way they build these battery packs in house so they have no problem adding custom connectors or what ever they can. I had them change mine out with the small tamiya connector to match with my Systema mechbox. So if you have the Orignal VFC gearbox and wires in there then you will need a small (mini Tamiya)connector as well, and need to re-wire the gun to the rear if you havent yet.
As for getting full trademarks like mine on a VFC you have had to have gotten it from Hong Kong, wich cost near $100usd just for shipping and the base HK416 DX itself was 505usd before shipping. And VFC wont email your back if you contact them there site is basicaly just for product veiwing and not comunication. Plus the tradmarks tecnicaly violate the law so VFC would not ship to you. My trademarks had to be covered with special glue/foam and removed once in my hands. Uses all M4 mags except C-Mag's wich you have to hevily modify like mine to fit the HK416's low and flaired mag well. I use the MAG(brand name) Heckler & Koch fully marked mid caps for mine, they work perfect. Anymore questions feel free to ask Ok I gotta head to the Univeristy now, so for give the sloppy post, Im time sensitive atm.