I am using an Arduino Uno on which I connected an xbee S2B module and an em-406a GPS. At first, I was using its usb port to supply it with power, but I want to make it a remote device so I connected a 9V of 280mAh battery. For some reason the Arduino doesn't work, not even a single led turns on for a second when it is connected to the battery.
Did you check that 9V source/connector is providing 9V? Center pin positive, the barrel (shell) negative? If that's correct, the problem is with the UNO.
I have connected it through the power jack and I have measured the battery's voltage and it gives me 9.6V, which is fine.
That battery seems small. Have you measured the battery output voltage while connected to the uno? Have you measured the voltage on the uno while the battery is connected?