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.
LilyPad Simple Power Hookup Guide
A basic guide for getting started using the LilyPad Simple Power with LiPo batteries.
PicoBuck Hookup Guide v12
The PicoBuck board is a high-efficiency three-channel constant-current LED driver.
Single Supply Logic Level Converter Hookup Guide
The Single Supply Logic Converter allows you to bi-directionally translate signals from a 5V or 3.3V microcontroller without the need for a second power supply! The board provides an output for both 5V and 3.3V to power your sensors. It is equipped with a PTH resistor footprint for the option to adjust the voltage regulator on the low side of the TXB0104 for 2.5V or 1.8V devices.
LiPo Charger Plus Hookup Guide
This tutorial shows you how to hook up and use the SparkFun LiPo Charger Plus board.