Shares of the Cupertino, Calif., tech major at last check were up 0.6% to $130.54.
Apple has been developing the attachment for at least a year and it has been scheduled to launch in the months after the iPhone 12 line is released, Bloomberg reported, citing people with knowledge of the product.
The iPhone 12 models were introduced in October.
The battery pack would attach to the back of an iPhone 12 using the MagSafe system, which all the new phones use for charging and pairing other accessories like cases and wallets.
Some prototypes of the battery pack have a white rubber exterior, said one of the people. The new accessory would differ from Apple battery add-ons for previous iPhones in that it only provides additional battery life and doesn’t serve as a full protective case.
In internal testing, the magnetic attachment system has proved strong enough for the charging unit to stay in place. But the accessory’s development has been slowed by software issues such as the iPhone erroneously indicating that the pack is overheating.
Apple also has been working to mend issues related to a customer switching between using the device on an iPhone with and without a case.
Sources told Bloomberg that given the new accessory’s development challenges, it could ultimately be delayed or scrapped.
Accessories and wearables have become an increasing source of revenue for Apple. Cases, AirPods, Apple Watches, home speakers and related products generated almost $13 billion, or 12% of total company sales last quarter.