I used the 7805 regulator recently with an AVR and LCD.
it did not deliver the needed power and the circuit did not work correctly(at least the LCD). I had to use power from usb.
the only reason i could think of was that the delivered current was low, although its rated for 1A in the datasheet
so why is that ??? and how can i get high currents from the regulator ??
one reason is , 7805 that you have got may not be rated for 1Amp.
if it is a TO-202 package then it can.
other reason , if you have TO-202 package and not getting 1amp is dueto:
--- because of (Vin-Vout) in 7805.
probably you would have used a 12v dc with 7805 to get 5v.
try to reduce the Vi to say 9v and see the output.
then it is not a 7805 problem. it is the 9v battery.
the 9v battery , that we get nowdays are fareastern origin and drains very quickly even for low current loads.
substitute a new 9v battery and see.
or have a regulated power supply.