Apple's 2019 iPhone lineup could include new iPhone models with significantly more battery capacity, according to a research note from TF International Securities analyst Ming-Chi Kuo.

If Apple were to include higher-capacity batteries in its newest iPhones, as predicted in the note, it could serve as a major selling point as iPhone sales growth has slowed in recent years. Some surveys point to battery life as the top reason that consumers upgrade to a new device.

Apple's iPhone lineup is expected to look a lot like its current lineup, according to the note. Kuo expects Apple to release a 5.8-inch iPhone (an improvement on the current iPhone XS), a 6.5-inch iPhone (like the current iPhone XS Max) and a 6.1-inch device with a lower-cost screen (which corresponds to the iPhone XR).

"Battery capacities of new 6.5" OLED, 5.8" OLED and 6.1" LCD significantly increase by 10%-15%, 20%-25%, and 0%-5% compared to last year's new models," Kuo wrote in the March 31 note.

The note suggests that the batteries would be the same physical size as this year's models, but they would have a higher power capacity in the same amount of volume.

One reason why Apple might stick larger batteries into its 2019 phones is that they could gain a two-way wireless charging feature, according to Kuo.

Two-way wireless charging would enable a user to place their AirPods, Apple Watch or other wireless-charging devices on the back of an iPhone and draw charge from it. Samsung and Huawei recently released phones with two-way wireless charging.

"Though the iPhone is not the first high-end smartphone to be equipped with two-way wireless charging, this new function could make it more convenient for users to charge the new AirPods and create a better integrated user experience of the iPhone and AirPods," Kuo wrote.

Kuo's research is aimed at investors who buy shares in the companies that supply Apple with parts, and he is well-known for predicting Apple products before they launch.

Apple usually launches new iPhones in September every year.

Last week, Apple cancelled AirPower, a wireless charging mat that was supposed to charge three devices at one time. It was originally announced in 2017.