You don't
need a special charger for the A123 cells. It is recommended to cut the charge at 3.6v/cell, so you could do it manually, or have a device like the LipoDapter do it for you:
http://www.slkelectronics.com/lipodapter/index.htm
You could use the Maxamps 2s 6000mah pack with a 7700. It would be fast :027: According to Castle you should be hitting about 40-45mph with that motor/battery setup.
You can safely run a 3s LiPo with the 4600 motor.
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