So i have a circuit with the sm5100b GSM/GPRS shield attached. now that everything is working I want to power it with out requiring my computer. Up to this point I have just been using it over usb which has worked fine. Now i have the system powered via a 12v battery attached to the arduino power supply plug. At 12 volt the arduino powers up just fine and my sketch begins to run, I have status LEDs to confirm this, however the sm5100b never reports anything back. If i use a voltage divider to bring the voltage down to 9v, lights are fairly dim, and it appears as though the arduino just keeps reseting itself.
Any ideas?