I have an Arduino set up to trigger my camera to take time lapse photos. Nothing complicated, just one IR LED firing a pulse every 15 minutes. My question is, what kind of battery should I use to last the longest in the field? I know 9V holders (with switch) are available, but I can't find one where I live. Could I use a 4 AA holder and solder on a 2.1 mm Barrel Jack?