To keep things simple, I'm going to refer to this year's iPhone X as iPhone X (2017), the successor to that as the iPhone X (2018), and the large-screen version of the iPhone X (2018) as the iPhone X Plus (2018).
Not too many specifics are known about the iPhone X Plus (2018) aside from that it'll have a larger, sharper display than the one found on the iPhone X (2017). However, there is one prediction about the phone that I'm extremely confident about that I'd like to share.
Bigger phone, more battery life
Since next year's iPhone X Plus (2018) is going to have a much larger screen than either the iPhone X (2017) or the iPhone X (2018), it will necessarily have a larger casing. That larger casing means that the iPhone X Plus (2018) will be able to house a significantly larger battery than the iPhone X (2017) does or the iPhone X (2018) will.
To put things into perspective, the iPhone 8, which has a 4.7-inch display, has a battery with a rated capacity of 1,821 milliampere hours (the larger this value, the more power the battery can store).
The iPhone 8 Plus, which has a larger screen and correspondingly larger casing, contains a 2,691 milliampere hour battery, which is 47.8% more capacity than the battery inside of the iPhone 8.
I think that the iPhone X Plus (2018) will have a similarly larger battery capacity than the ones in either the iPhone X (2017) or the iPhone X (2018).
That increased battery size should mostly translate into better battery life, which is something that a lot of smartphone users care about.
The reason that the much larger battery won't translate into much longer battery life is simple: Power requirements scale with device size.
The iPhone X Plus (2018) will have a larger screen than either the iPhone X (2017) or the iPhone X (2018). This means that if the iPhone X Plus (2018) had a display that had the same pixel density as the display on the iPhone X (2017) or the iPhone X (2018), then it would still have more overall pixels.
More pixels mean greater power consumption, which ultimately translates into lower battery life.
To further compound the issue, the iPhone X Plus (2018) is expected to have a slightly sharper display than the iPhone X (2017) and iPhone X (2018). This means even more pixels on the screen that draw power and chew up even more battery power.
That's one of the reasons, for example, that the iPhone 8 Plus doesn't feature nearly 50% better battery life than the iPhone 8 -- the battery capacity gain relative to the iPhone 8 is being split between improved battery life, a larger display, and a sharper display.
Now, to be clear, this is by no means meant to be a jab at Apple. I think that customers care about display image quality and if the company can deliver a sharper display while retaining similar battery life, then that's a clear win for iPhone buyers.
Ultimately, everything in engineering is about managing a complex set of trade-offs to deliver the best user experience possible in a reasonable cost structure. I believe Kuo's claim that the iPhone X Plus (2018) will have a larger and sharper display than the iPhone X (2017) and the iPhone X (2018), but at the same time I don't think all the battery capacity gains will go toward the better display -- I think the iPhone X Plus (2018) will have a clear battery life advantage over the iPhone X (2018).
The improved battery life of the iPhone X Plus (2018) compared to the iPhone X (2018) should make the former quite compelling to Apple's most enthusiastic iPhone customers, ultimately driving said customers to buy the larger, more expensive iPhone over the smaller, cheaper iPhone -- something that'll help fuel Apple's iPhone average selling price growth story.
Ashraf Eassa has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Apple. The Motley Fool has the following options: long January 2020 $150 calls on Apple and short January 2020 $155 calls on Apple. The Motley Fool has a disclosure policy.