Well first off the batteries capacity will be the same whether parallel or series Example: 3 2500 mah 18650's = 27.75 watt hours no matter if parallel or series. The board will only draw up to 23 amps from the batteries but because it's a buck converter it will output as high as 55 amps @ 9 volts. Edit: besides it won't work, 7.4 - 11.1 volt pack yes, 3.7 volt pack no.