Lead acid batteries are rated in "Amp Hours".  Theoretically, if you have 1 Amp Hour (AH) battery, then you can run a 1 amp device for 1 hour. And if you have 2 AH battery you can run a 2 amp device for 1 hour (or a single 1 amp device for 2 hours). But in reality the method of measure is not strictly defined and battery manufacturers often stretch the numbers.  Better to go with the largest AH battery that will fit into your applicaiton. 

 Our 12V high Torque Prop Motor draw a maximum of 3 amps.  So technically, a 3 AH battery would run the motor for 1 hour.