problem with dell truemobile 1350

i have the 1350 card in a inspiron 1100,  if i keep the ac cord plugged in wireless is fine, however if i go on battery power, the activity light on the card starts flashing pretty fast and browsing the net is almost impossible, on the other hand just as soon as i return to ac power all is fine again.   anyone have any suggestions or should i just call and get a replacement card sent to me as its still under warranty?