Yes you can. Remember to connect the batteries serially, not in parallel. That is + electrode of one cell should be connected to - of the other, while remaining two electrodes should be connected to the circuitry.
Since you said that the system is outdoors: do your budget and the environment a favor and use solar power, so that you will not need to change the batteries in the foreseeable future. The easiest way is to buy some solar garden lights and connect your circuit in parallel to the batteries. It should be quite affordable.
Tunc
(published on 12/20/2015)
