multiple 12V DC motor with arduino uno and L293 h-bridge

I am making a tracked robot and am running into a problem when running the 2 12V DC motors. I have my circuit wired to work with 2 smaller 6V motors and it works fine. For the 12V motors, I have a 12V battery that I use as an external power source for the motors. The L293 datasheet says it will support up to 36V, at less I read it wrong. However, when I run the sketch, the 12V motors don't function right, then stop don't move. I think it has something to do with the power source and or the h-bridge (L293) I'm using.

Any advice for using 2 12V DC motors would be appreciated.

Is it possible that your motors require more current than the L293 can control? Check the specs on the chip and the stall current on the motors.