Does the battery connector from the gun actually lead out through to the handguard area? Pics look like there's plenty of room for a mini in the buffer tube.
It comes with a hi-cap mag. Unless it's similar in design to the TM M4 hi-caps that can unload a full mag on one full proper wind, you'll find you're going to have to tickle it occasionally to keep it feeding properly. That isn't uncommon.