Charging a battery with a battery and a motor controller

I have an RC car that uses 2 parallel 5 series A123's and want to be able to quick charge the pack. I was thinking about using one of my 10s 1p packs as a power source and then using a motor controller to regulate the charge current to around 16 amps. I can watch the voltage and mah and then cuttoff when nesessary. I will then take the battery and charge it the last 20 % or with a balancer and a proper charger. Will this work? Beside the danger of over charger is there anything I need to worry about?