Not true, when balance charging the charger supplies engergy through the manin charge leadn and continues to do so as the charger enters the balance phase. The balance tap is only used to bleed off excess energy. When one cell reachers 4.2 volts the charger lowers the charge rate and discharges that cell while charging the other cells. When all cells reach 4.2 volts the charge is finished. There is a bit more that the charger calculates to determin the end but that is basically it.

When shopping for a charger, take a look at the current drain for balancing spec. that is a good indicator of how fast a charger will be able to balance a battery. My iChargers have a current drain of 350ma for balancing. Not the best but they do a great job. I have seen some that will drain up to 500ma and I am sure there are more.