good luck
lets pretend the motor is rated for 12v and draws 400ma (as per the specs), and you have that 5200mah of battery (2x 2600), so you should get 5200 / 400 = 13 hours of runtime
400ma is for a free running motor, the datasheet says 6 amps for a stalled motor, which would mean a little less than 1 hour of runtime
but in the end, the motor is not rated for 12v so it will fry soon