Well mAh isn't an amp rating, it's a battery capacity, more a measure of energy than of power (if we take amps as an analog for power at fixed voltage, and ditto Ah as a measure of energy).
The real question I think you should ask is, can the battery supply enough current for your motors, which depends on the motors not the shield, and which you didn't mention.
You also need to consider the fact that a 298 drops a minimum of 2V, and that becomes almost 5V at higher currents, so is there enough left of your 7.2 to turn your motors?
That all said, the attached shot from the 298 datasheet tells you its maximum voltage and current.
