Full metal shell, rechargeable lithium-ion battery, and it can work with incoming calls. The FiiO Rocky E02i ($29) is a brilliant and sleek nifty little headphone amp that will improve the overall audio quality of your headphones or earbuds of choice. Better is NEVER louder in the recording world, so you should get a smoother and clearer dynamic listening experience with a touch of much needed thump, so there’s a good chance that this little devil will make some MP3s sound closer to CD quality .wav files. And the price can’t be more modest for under $30. If you are an audiophile and are used to shelling out some serious capital for improving the sound on a pair of $1000 headphones, then this might NOT be what you’re used to, but you gotta admit, it’s convenient and user friendly!