MAX1870A is able to achieve better than +/-1% accuracy with +/-1% resistors by reducing the adjustment range of the battery voltage and taking advantage of ratiometric scaling. The BATT voltage adjustment range is limited from 4V to 4.4V, so any inaccuracies only affect about 10% of the output voltage. Moreover, VCTL is ratiometric with respect to REFIN, so inaccuracies in the reference voltage are negligible. The total charge voltage is multiplied by a precision scale factor determined by the number of cells used. For more information regarding about the charge voltage, consult the "Setting the Charge Voltage" section on page 18 of the MAX1870A datasheet (19-3243).