I am sure you have seen this thread :):
http://forums.radiocontrolzone.com/s...d.php?t=203178 (you are b3racer there, right?). Read Bob Novak's comment.
I don't think the MGM controllers can go as low as 4cells. Even if it could, you should still use a RX pack, as 4.8v will drop, and so will the BEC voltage.
SH Z-Car, Custom Crawler, 8s Savage,
12s XTM XLB 1/7 buggy,
4wd 4-link rear/IFS Pro4 truck,
Custom Hyper 10 Short Course,
Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz