Huge gearedmotor

i have two geared motors but it isn`t small like normal geared motors that you use ,it`s huge ( in fact it`s a car with two geared motors one in each side ) ,so when i connect the two motors to  two 9v batteries in series it works very short time like a minute or something ,then the batteries is dead , what can i do ?????

please help.

 

or even

Loads of AA batteries in series(rechargeable if possible)