Power Problems when Driving a motor

II'm using a Uno board, and a DFRobot L298 shield, to power 2 Tamiya motors. I'm using a standard 9V battery, (6LR61), connected to Power in of DFRobot and Power of Uno Board. I can see Uno running, due to the leds on card, with expected behaviour. However, it does not activate the motors. The ground of both cards are connected, and when I connect the USB to Uno, it drives the motors. I measured the Vin of Arduino, which shows 4.8 ~4.9V. Any Idea about what is going on? It's my first Arduino project, so sorry if it's a stupid question. :~
Thanks in advance,

A 9V battery is usually under-powered to drive motors. Try using a 7.2V AA battery pack, or a power supply, etc. Or just try 1 motor for now.

The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

Alkaline PP3's are no good for high current work at all. Don't try to take more than 50mA from them.

Possibly NiMH or lithium ones might work, but really if you driving motors and need 9V, you need a PP9 battery.

Thanks for your support!
I tried two independent power sources (with GND connected), and it worked. Besides, I realized the 9V battery does not fit for this application as you stated. I`m gonna buy a NiMH battery for my project.