12C... that's 84A... show me the charger...! For the now-average 6000 cell, 2C is 12A - show me the charger...!!
Look at any thread here recommending chargers and the highest you can get out of most of them is around 7A-8A. Spend mega-bucks on an LRP and you only get 12A!
The reality is that the charge time isn't reduced that much. The longest part of the charge is the last bit at constant voltage. The more amps you charge at the quicker the cell reaches its max (4.2v/cell) and the longer it takes to top out to full charge.
It may be that if you fully discharge the cell and then re-charge it so it gets a bit of heat in it it will give a bit more punch, but the reality is that only full Mod in a TC or 12th will take more than 3500ma out of a cell. At that level, anything over 8A will get it to 4.2v/cell in a few minutes, and then it spends the rest of the time on CC phase very (very!) slowly getting to full charge.
1C up and down for best life and good performance - simples...! HTH
