Okay so I have an UNO that has an nrf24l01+ attached. I want it to be completely wireless so free of the 5v USB power and the 12V wall plug. In this case what can I use? I do not wish to plug the power directly into the Vin as I am relatively new and afraid that it might fry the board. So I wish to plug it into the barrel jack. So I have read that using a 9v battery to power UNO is a waste of power as most of the power is translated into heat. Also, using 4 AA batteries seem to be a good solution except that I'm not sure if it has enough power for nrf24l01+ as I've read that an arduino with nrf24l01+ on batteries creates an unstable wireless node. I would like some help on what I can power the UNO with.
I've used the usb battery chargers (marketed to recharge cell phones) with great success on many different Arduino boards. They come in a variety of mAH capacities and are easily recharged with any powered USB port/power adapter.
Here's a link to one I've used. (I'm not affiliated with Duracell in any way).
Firstly if you only need short runs, go with the usb battery pack answer, but if you need the longest time from least batteries:
As has been pointed out, for best battery consumption an arduino board is not efficient due to power regulators and led lights. For best performance you want a standalone 328 chip with its BOD (brown out detector) reduced to 1.8v and then you can run it and the nrf24 chip off 2x AA batteries.
But all this might be a bit beyond you.
One thing though that will help your battery life is a PNP transistor or Mosfet on the +ve of your nrf24l01+ module triggered by a arduino io pin. as these power amplified versions dont sleep (per say, the chip does but not the PA) so it will always be consuming a large amount of power regardless of state. So just use your io pin to power it on and off for each use.
(that is unless you need it on always for recieving, in which case this wont help)