After removing the the upper and lower parts of the chassis, we began to disassemble the lower part, which contains the main board and a secondary battery, by taking out the screws that fix the main board (See related article 1).

"Why on earth does it have this many screws?" an engineer said. "There were only two screws on the outside."

There were total 20 screws fixing the main board on the chassis. After we managed to remove all the screws and take out the main board from the chassis, a secondary battery appeared.

It was a Li-polymer secondary battery, like the one equipped in "iPhone 2G" (See related article 2). Its supply voltage was +3.7V, but the volume of the battery, etc were not printed on it.

Looking carefully at the battery, we found that it was connected to the main board by using a dedicated terminal, like the batteries in Japanese mobile phones. In the iPhone 2G, its main board and Li-polymer secondary battery were soldered.

"Probably, Apple used the dedicated terminal to improve the workability," said one of the engineers.

At this moment, unexpected words came from another engineer who was examining the Li-polymer secondary battery.

"The battery does not come off the chassis."

The Li-polymer secondary battery was so firmly attached to the chassis that it did not seem to be easy to remove the battery.

"The secondary battery is placed in the innermost part of the chassis," engineers said. "Is it possible to replace the battery?"

iPhone Teardown Video (Part 2) (Japanese, 3:57)