When powering a Nrf24L01 hooked up to an arduino by external battery does ground still go to the Arduino ground?
The GND of the battery and the Arduino shoud be anyway connected together so it does not matter. 
Connect it that way and the Arduino to the battery (Vcc to 3.3V the data-pins are 5V tolerant):


An example pin-connection would be (but this depends on your code):



For the Nano this might help: