You did not say if the batteries are lead-acid, Ni-Cad, Ni-MH or Lithium.
Ah is not the maximum Amps a battery can produce, it is how long the battery can produce a certain low current.
A 50Ah car battery can provide 600A (!) to the starter motor on a cold day when the oil is thick. The Lithium batteries for my radio controlled model airplanes can provide 70 times their Ah rating.
The drill uses a high current when it is working hard. If you use a weak power supply then it will not be able to work hard.