An early teardown of the iPhone 5s and 5c, conducted by iExperts in Australia, has a exposed a few notable details about the hardware. It confirms for instance that the 5s has a new connector for the Touch ID fingerprint sensor assembly, and that while the 5s has a 5.92Whr battery, the 5c uses a 5.73Whr part. The original iPhone 5 battery was rated at 5.45Whr. At least in the phones iExperts received the new batteries are stamped "Apple Japan," hinting at possible suppliers.
More immediately significant is that Apple has added an extra layer of coating to switches, which iExperts suggests
should prevent internal failures seen in previous iPhones. Though iPhones are generally considered reliable, they can still be subject to defects, In case of a defect, Apple will typically replace an iPhone outright if it's still on warranty.