Choosing a battery...

[MetalMan]

You could take two 5s packs and run them in series, and charge them individually. But, the A123 cells are most likely connected together using thin (welded) nickel strips, so you'll want to rebuild the pack. Just make sure that if you do this all of the tap wires go where they were before you disassembled the pack.
I haven't read anything special about the A123 cells. What I have read people seem to be saying that these cells are similar to the Emoli cells in that after a certain current is passed, the voltage starts to sag (~35amps for the Emoli cells). The A123 cells are a lower voltage, their max charge voltage is 3.6v, compared to Emoli/Lipo of 4.2v. That puts the nominal voltage of the A123s ~3-3.2V. And I still haven't read anything on them about LVC voltage if it's necessary and if so at what voltage it should be set to.