A report from Asia reinforces the speculation that a lot of Apple's focus is on thinness for the rumored iPhone 6.
"But both feature a similar capacity," the report added. If true, that would indicate an emphasis on thinness over capacity -- boosting capacity can indicate an increase in the size of the battery.
The Digitimes report echoes a report in April from Commercial Times, also a Taiwan-based publication, that claimed the larger 5.5-inch iPhone 6 would have 2 mm-thick battery.
Overall, Taiwan-based component makers are "facing difficulties" reducing the thickness of components including panels, chassis, and battery packs for upcoming iPhones, Digitimes said. Those difficulties stem from trying to make thinner parts but not achieving satisfactory production yield rates (the ratio of good parts to bad parts).
The Digitimes report adds to a growing list of reports that highlight the challenges Apple and its chain of suppliers are facing to create the thinnest iPhone to date.
And earlier reports cited issues with a new backlight, which would also contribute to a thinner phone.
Digitimes added that 60 million to 70 million new iPhones are expected to be sold by the end of 2014.