eBay is offering an iPhone 4 / 4S 2500mAh black battery backup case for only $10 with free shipping. Other colors are available but are slightly more than the black model. Each case also includes a free screen protector.
This External Power Battery Pack and integrated case for iPhone 4G and 4S is an ideal and powerful companion for your iPhone. It acts both as a protective case and also as an excellent external battery pack. The powerful built-in 2500 mAh Lithium-ion Polymer battery can be engaged using the On/Off switch button at your will and it is able to provide additional talk time by up to 6~7 hours for your iPhone4/4S and additional standby up to 5 days
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