There are plenty of accessories designed specifically for Apple's various portable devices in general and the iPhone in particular available out there, on the market, but the most useful of them, by far, are those capable of enhancing the smartphone's functioning life via a built-in battery.
And, in fact, that's exactly the type of product you'll read about as follows, namely the Proporta TurboCharger Back Pack (Apple iPhone 4), a protective case that, similar to some other accessories of we've previously encountered, comes packed with an included extra battery.
Using the device is actually a pretty simple task, according to Proporta, since one will simply have to insert their iPhone 4 into the Back Pack by separating the two sections and then sliding them back together once the iPhone is in place.
After they're done with this part of the process, the Back Pack will automatically commence charging the handset from Apple and they'll be able to see the charging icon appear on the iPhone.
Furthermore, in order to keep the users informed regarding just how much juice there's left within the extra battery, an LED display shows the level of charge (this is pretty important, actually, since it ensures the fact that users won't be caught off-guard, with a depleted phone battery).
Last, but certainly not least, we'll have to point out that the rechargeable battery found within Proporta's TurboCharger Back Pack provides an impressive 1700 mAh storage, which is apparently quite enough to charge the Apple iPhone 4 more than once.
Now, of course, such an useful accessory won't exactly come cheap, or at least it will cost a bit more than an usual protective case, as the Proporta TurboCharger Back Pack for Apple iPhone 4 sells for somewhere in the vicinity of 66.95 US dollars, a price tag that, nevertheless, is slightly under the average market level for this particular type of products.