You can use an individual backup battery to charge your smartphone, but if you use Samsung Galaxy S3, mophie juice pack Samsung Galaxy S3 case should be more suitable for you.
This is a durable, practical battery case that measures 5.91 x 2.97 x 0.67 inches, weights 1 lbs, and designed for Samsung Galaxy S3 Android phone. As we can see from the images, the Samsung Galaxy S3 case features gorgeous ultra-thin, form-fitting design, and the durable, two-piece construction effectively protects your Galaxy S3 from bumps and scratches, and custom cutouts allow you ease access to all buttons and functions of your Galaxy S3. Most importantly, the Galaxy S3 case also features a built-in 2300mAh backup battery that can offer you up to 9 hours of extra talk time on 3G or up to 7 hours of talk time on 4G, moreover, the standby switch lets you charge your smartphone only when you need it, and the LED indicator intuitively shows you the battery status.
Mophie juice pack Samsung Galaxy S3 case with backup battery is available in two colors including white and black, each one is priced at $99.95 USD. If you’re interested, jump to mophie official site for more details or check out the following demo video first.
Additionally, if you need other options, you might like to check PowerSkin Samsung Galaxy S3 case.