(Yicai Global) Oct. 9 -- The latest iPhone 8 produced by Apple Inc. [NASDAQ:AAPL] has just come out, but users are already complaining about battery swelling causing cracks on the edge.

An iPhone 8 user in Guangzhou in China's southeastern Guangdong province recently complained to Yicai Global about the problem.  

Wang Ting (a pseudonym) told Yicai Global her husband ordered an iPhone 8 Plus online as a gift for her on Oct. 3. After getting the phone the next day, she found a crack on the edge from a battery swelling defect.

This model is the 64G gold iPhone8 Plus, and the crack was on the edge of the screen on the SIM card side, resulting in the slight exposure of the internal components, but with no sign of combustion, Wang said.

Yicai Global called Apple's service line, whose staff member responded that the phone had been sent back for maintenance on Oct. 6. However, instances of cracks appearing on the edge caused by battery swelling are few, the staffer claimed. "At least this is my first case. It's possible that it occurred because of an impact in transit or during delivery."

However, 'crack' cases reported online show similar occurrences in Taiwan, Japan, Canada, Greece and other countries and regions.

The crack problem with the new iPhone model is neither a design defect, nor a problem of inferior quality, but is caused by the frame structure of the iPhone 8's metal frame and glass back cover, Sun Yanbiao, an expert in mobile phone supply chain manufacturers, told Yicai Global.

After the battery heats, the swelling is a normal phenomenon, Sun said. "The glass expansion is relatively small, but once the battery swells, the glass and the screen metal frame will crack. No such problem arises with the models with metal frames."

He believes the mass shipments of iPhones boosts the probability of the problematic iPhone. "In fact, a few millionth of this kind of massive quantity in the supply chain is allowable," Sun said.