A123 systems sell two different models of hypersonic charger:
http://www.a123racing.com/html/soniccharge.html
The bigger one will do 2-3 "hypersonic packs only", whatever thats ment to mean. I would guess though that the charge current may simply be reduced if you plugged in a 2p pack, rather than a 1p pack, same as with any other charger, depends on its output power and the power supply...