Did you look at the motors specs on Banebot's web site??
The No load current is 1.4A and max current is 85A.
How long does it run from after changing the Batteries??
If 10minute (1/6 hour) and with a 1.2A-Hr battery means that the motors are drawing about 7.2Amp which is well within the Banebot spec. These motors can draw much, much more current than this.
Have you measured the actual current draw of the motors?
Do this then divide the battery's capacity by the average motor current to find the number of run hours expected.
The Sabertooth has these specs:
Out of the box, the Sabertooth can supply two DC brushed motors with up to 5A each continuously. Peak currents of 10A are achievable for short periods. Because Sabertooth 2x5 incorporates soft current limiting and thermal protection, you need not worry about killing the driver with accidental stalls or by hooking up too big a motor.
So the Banebot motors can draw much more than the Sabetooth will allow. It will of course either current limit so you should not hurt the Sabertooth.
Have you read the Sabertooth manuals? It says about the error light this:
The red LED illuminates if the Sabertooth has
detected a problem. It will light if the driver has
shut down due to a depleted battery or due to overheating or overcurrent. If you are using a NiCd
or NiMH battery, and commanding an acceleration causes the motor to jerk and the Error LED to
flash on and off, the battery is depleted.
And from my above calculations it seems to be the battery is depleted.
What is the battery Voltage when the error light comes on??