 The iPad 2 has a 25 W · h rechargeable lithium-ion polymer battery that lasts 10 hours, like the original iPad. It is charged via USB or included 10 W, 2 A power adapter. The battery is 2.5 mm thick, 59 % smaller than the original and has three cells instead of two. The improvements allowed the injection-molded plastic support frame to be omitted. The 10 W USB power adapter provides 4x the power of a conventional USB port. The tablet has an audio frequency response of 20 Hz to 20 kHz. Without third-party software it can play the following audio formats: HE-AAC, AAC, Protected AAC, MP3, MP3 VBR, Audible formats (2, 3, 4, AEA, AAX, and AAX +), ALAC, AIFF, and WAV.
