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.
Wake-on-Shake Hookup Guide
A basic hookup guide for getting started with the SparkFun Wake-on-Shake. The board gives you the ability to put your project into hibernation until bumped or shaken awake using the ADXL362 accelerometer. This means you can design projects meant to stay inert for long periods of time, possibly even several years, depending on the battery type used to power the project.
Photon Battery Shield Hookup Guide
The Photon Battery Shield has everything your Photon needs to run off, charge, and monitor a LiPo battery. Read through this hookup guide to get started using it.
Nuclear Battery Assembly Guide
How to put together your BYOT (Bring Your Own Tritium) Nuclear Battery Kit!
SparkFun Qwiic Quad Solid State Relay Kit Hookup Guide
A Hookup Guide to get you started with the SparkFun Qwiic Quad Solid State Relay Kit (say that five times fast!).