Though I haven't really had much time to test it out so far, here are some first impressions of this $24 External iPhone 4 battery pack I got from eBay. Listing link. Feel and build quality Compared to other batteries I've ordered from overseas, this one feels the best. It is smooth to the touch and easy to grip. The top piece slides off so you can easily slide the phone in. However, aligning to top piece when putting it back on takes more effort than it should. One thing I like about this case in contrast to other cases, is that this one uses the same 30-pin connector the iPhone uses. Convenient, right? Sort of... Not all USB cables will fit. I've attached pictures of me trying to plug in two USB cables. One is the official cable from Apple (which fits), and the other is a generic cable, which appears to be identical to Apple's. The generic cable did not fit. Signal One issue with many generic batteries is covering the antenna, thus losing signal. This case does NOT have that issue. I used the Cydia app "Strength" to measure the signal, and there was no difference with the case on or off. Camera Let me just say... Using flash will RUIN your photos if you have this case on. I'll attach photos in another post. In normal light photos, there is a small curved shadow at the two bottom corners (in portrait orientation). Sound System sounds (locking, unlocking, etc) sound slightly muffled, but when it comes to music, it sounds the same (if not better). I tested the microphone with and without the case. There was maybe a slight volume decrease with the case on. Nothing substantial. Performance I haven't had the chance to test the battery in the wild yet, and I won't really have a practical use for it unless I go on vacation and won't be able to charge it for a while. However, tomorrow I'll put the battery to the test by leaving my iPhone in it from midnight and seeing how long it takes to discharge. I'll update my post tomorrow. EDIT: Battery Test I Normally, I keep my phone charging all night and unplug it at around 7:30 AM before I go to school. During school, I text regularly, take some photos occasionally, listen to music during lunch/gym, lots of web browsing, etc. At 3:00 PM, I normally have about 50% battery left. I should also note that I have various tweaks running constantly such as SBSettings, LockInfo, iRealSMS, etc. For my first test, I charged the battery pack completely. One that was charged, I unplugged it from the wall, and put my iPhone into the battery pack. The phone already had a 90% charge. Before I went to sleep, I played some games, checked Twitter and Facebook, and used iBooks for about a half hour. I went through my day of school doing the same tasks I mentioned above. At the end of school, my iPhone battery was still at 100%, and the battery pack was still powered on. At around 5:00 PM, the iPhone stopped charging and was at 100%. Tonight, I'll completely discharge my phone and see how much it will charge tomorrow morning and throughout the day.