Charge them for 15 hrs with a wall charger that has a rate of around 350-400 ma. The chargeing at c/10 does the balancing.
Since you have 8 cell packs then a wall charger that is for 9.6 volt batts and around 200-500 ma can be used to charge. The total time (in hrs) just has to be figured by dividing 5700 by the rate of the charger.