The iPad Pro has four big speakers which, according to the iFixit teardown, take up space that could have been used for battery.
Every time Apple releases a new device, iFixit tears it down, taking a look inside and seeing what's what. The insides of the iPad Pro look similar to every other Apple tablet, except for the much larger speaker cavities that sit at the four corners.
iFixit
The iPad Pro has four big speakers and two smaller batteries.
Apple describes the speakers as "innovative," arguing that the new, bigger design gives "the speakers 61 per cent more back volume compared to previous iPad audio designs." Considering that the iPad Pro is aimed at replacing a laptop, having good speakers is a trade-off.
iFixit concludes that "it appears ... the Pro's self-balancing, four-speaker audio comes at the cost of battery capacity" even if the sound quality is better.
The iPad Air 2 has two speakers at the bottom of the device, leaving far more space for the battery.
iFixit
The iPad Air 2 uses far less space for speakers.
Apple claims that the iPad Pro gets around 10 hours of battery life which was seemingly confirmed by various reviews of the device.
John Gruber of Daring Fireball argues that the increased speaker size isn't an issue because battery life is already good and reducing the speaker quality would be worse than decreasing battery life.