From the examples I saw by Felix and other people here, I honestly thought that with my simple sketch 3xAAA would power the moteino for at least 1 year no problemo..!
Yes, you can get one year from AAA batteries if you work at it. A AAA battery will supply approximately 1200mAH, which, if you want to run for a year, means that your average current needs to be less than 137uA. Wow, that's a lot! However, it's not a lot if you're using 8second power off intervals with 10s of mS on times (where ON = 16mA or more). After you work on this a bit, you should be able to get below 25uA average current, but you need to understand what it takes to get there.
The recipe for maximum battery life is knowing:
1. how much power each of your devices consume when ON and when sleeping.
2. knowing how often you NEED to send data. Does the parameter you're sensing really need 8 second sampling time? What will you do will all this data?
3. knowing and being able to control when each device is ON and when it's sleeping or OFF.
4. running your processor at a speed commensurate with the task. If you're just moving data, 8MHz or less is sufficient (hint: 8MHz is a very important number)
5. providing just enough voltage to perform the task and devices you need. Do you need 4.5V? I doubt it.
6. learn enough about battery technology so you know what kinds of batteries will supply the voltage you need without wasting power reducing too much voltage to the voltage you need.
Others have provided good tips for the programming side if you understand this basic recipe.
AND, finally, good for you for asking questions and welcome to the 'clan'!
Tom