The 5s has a claimed 10 hours of talk time on 3G, but there are rumbles that iOS 7 isn't doing you any favors.

The gold unit from Desay Battery Co., Ltd in Huizhou, China sports a 3.8V - 5.92Wh - 1560 mAh battery. Comparatively:

iPhone 5: 3.8 V - 1440 mAh - 5.45 Wh. Talk time: Up to 8 hours on 3G. Standby time: Up to 225 hours.

Samsung Galaxy S4: 3.8 V - 2600 mAh - 9.88 Wh. Talk time: up to 7 hours. Standby time: Up to 300 hours.

Motorola Moto X: 3.8 V - 2200 mAh - 8.4 Wh. 24 hours of "mixed usage."

It appears different units sport different battery manufacturers; our "space-gray" spare (right) comes to us from Simplo Technology Inc.