Part of The definitive guide to open source hardware projects in 2009

Energy, Power and Green – These open source hardware projects power things or have something to do with powering devices, saving the planet and monitoring power/energy in some way.

Smart Battery Meter
Pt 2382
The Smart Battery Meter measures the “state of charge” of a 12 volt or 24 volt sealed, lead-acid battery system. It uses a multi-color array of LEDs to give an instant visual indicator of the remaining charge, sort of like a gas gauge.
Price: $24.95
Visit the project page

Adjustable breadboard power supply
Bbpsup Lrg-2
This project details the design of a very low dropout adjustable power supply. A good power supply is essential to electronic projects. While there are many existing designs for adjustable power supplies, this one makes improvements that make it more useful for hobby designs.
Price: $15.00
Visit the project page

Botanicalls Kit
Botanicalls Kits let plants reach out for human help! They offer a connection to your leafy pal via online Twitter status updates to your mobile phone. When your plant needs water, it will post to let you know, and send its thanks when you show it love.
Price: $99.00
Visit the project page
Buy one @ Maker Shed

MintyBoost Kit
 3037 2737053545 Fd1196A788
Build your own MintyBoost: a small and simple (but very powerful) USB charger for your iPod or other MP3 player, your camera, cellphone, and any other gadget you can plug into a USB port to charge.
Price: $19.50
Visit the project page
Buy one @ Maker Shed