iPhone 6 with 4.7-inch screen is reportedly gunning for a September release date.

Latest reports claimed a bigger iPhone will be released this year. But a much bigger iPhone phablet will be launched at a later date.

Apple Insider cited Taiwan's Commercial Times saying Apple was having trouble fitting the ultraslim battery into the new device. There were also claims saying Apple will need a battery that is less than 2 millimeters for the phablet version of iPhone 6. This is less one-third less than the size of battery currently used in iPhones.

Apple seemed to have an issue among the company's manufacturing partners, which include Samsung and LG Chemical. The phablet was expected to ship later and the battery issues could be part of the reason.

Reliable KGI Securities Analyst Ming-Chi Kuo, who has an impressive track record in predicting Apple's plans and roadmaps, said earlier this month that Apple will release a much bigger handset in the fourth quarter of this year, months after its smaller version was launched.

Reuters reported the company was working on two iPhone 6 models. One smartphone will pack a 4.7-inch screen panel and be the successor of iPhone 5S. The other variant will boast a 5.5-inch display and start a new smartphone line that will dive in the phablet category. Other rumored features of the handset were faster A8 processor, iOS 8 and touchID fingerprint sensor.

Meanwhile, Cult of Mac reported Piper Jaffray Analyst Gene Munster expressed his concern that iPhone 6 phablet may cannibalize the sales of iPad Mini. In his note to the investors, he said consumers may update to iPhone 6 if it will pack a bigger screen display than keeping an older phone and buying an iPad Mini. Others may also opt for an iPad Air.

Apple has always been cool about cannibalizing its own sales. In February 2013, Tim Cook told investors that "if we don't cannibalize, someone else will," which could be the primary reason Apple is not worried in cannibalizing its own sales.