Portable power for an UNO with a nrf24l01+ attached?
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).

http://ww2.duracell.com/en-US/product/instant-usb-charger.jspx