After using this in one of my other projects (wireless tank gauge) , ive come to find something i overlooked and did not notice in my initial use. While the 328p (1.8v-5.5v) will happily run off 2xAA (or AAA) batteries either Alkaline or NIMH the NRF24 is a little more fussy, and is rated for 3v3, apparently though it can handle 5v logic connections but the vcc must be 3v3. So as my 2xAA NIMH started to discharge it cut out at 2.6v, so its more suited to the upper charge states of 2 alkalines (2.6v-3v), or 3 nimh (2.8v-3.6v).