Reducing Arduino Power Consumption
Contributors:
Alex the Giant
Alex the Giant 
Resources and Going Further
More information on low-power modes and options can be found in the datasheet for the 328P.
For more power-related fun, check out the following SparkFun tutorials.
Sunny Buddy Solar Charger V13 Hookup Guide
How to hookup the Sunny Buddy: a solar-powered, MPPT (peak-power tracking), LiPo battery charger.
Buck Regulator Hookup Guide
Get started with SparkFun's newest Buck Regulator Boards - the BabyBuck and the Buck!
LiPo Fuel Gauge (MAX1704X) Hookup Guide
Monitor your LiPo battery with the LiPo fuel gauge! In this tutorial, we will be using the MAX17043 and MAX17048 to monitor a single cell, LiPo battery over the Arduino Serial Monitor. We will also connect a display to view the output without the need to connect the microcontroller to a computer.
Breadboard Power Supply Kit 5V/3.3V Quickstart Guide
Quick start guide for the Breadboard Power Supply Kit 5V/3.3V