Buy.com’s Deal of the Day is the Tekkeon myPower MP1200 Smartphone External Battery (model no. MP1200) designed for the iPhone 3G and 3G S. It was once priced at $79.95 but has dropped $39.96 and is now available for only $39.99, with FREE ground shipping also included. Sales tax applies for residents of New York and California.

Add $5 and upgrade to the EnerG Slim-Fit Extended rechargeable battery case for the iPhone 3G and 3G S, offering three additional hours of video playback and four hours of internet usage over the featured product, but providing less protection than the Tekkeon case. It’s located at Amazon.com for the discounted price of $44.99 and has shipping rates starting at $3.99. Enhance your listening experience with the Altec Lansing Orbit Ultra-Portable Speaker for iPhone or iPod systems, priced at only $9.99 and available at Macmall.com, it has shipping rates starting at only $5.99 for ground delivery. Amazon.com also has something for all you car owners out there, the FlexPod X2 Premium Car Mount System with Auto-Seek Signal Intensifying FM Transmitter. Previously listed for $119.99 its now priced at only $59.99 and has ground shipping rates starting at $7.99.

The Tekkeon myPower external battery and case is designed to both power and protect your iPhone simultaneously. It delivers a rechargeable Lithium-ion battery that takes up to three hours to charge by itself, or roughly 6 hours with an iPhone, and provides  approximately 5 hours of additional talk time, or 7 hours of video, 24 hours of audio, or 6 hours of Wi-Fi. It also includes a bypass feature which enables it to preserve the iPhone battery until the device is out of power. The battery comes backed by a full-one-year manufacturer’s warranty. Dimensions: (W) 2.6” x (L) 4.9” x (D) 0.8”; weight 2.5oz.