Apple this evening announced a rare revision to its Q1 2019 earnings guidance. The company adjusted its revenue expectation to $84 billion, down from its previous guidance of between $89 billion and $93 billion. Following that announcement, Tim Cook went on CNBC to offer a bit more color on things.

First, Cook reiterated much of what he wrote in his “letter to Apple investors.” The Apple CEO explained that “over 100 percent” of AAPL’s shortfall is from iPhone, and primarily due to performance of the device in Greater China:

If you look at our results, our shortfall is over 100 percent from iPhone, and it’s primarily in Greater China. As we look at what’s going on in China, it’s clear the economy began to slow there for the second half. What I believe to be the case is the trade tensions between the United States and China put additional pressure on their economy. We saw, as the quarter went on, things like traffic in our retail stores, traffic in our channel partner stores going down, the reports of the smartphone industry contracting.

Cook also explained that factors such as foreign exchange and the lack of carrier subsidies are affecting iPhone demand. Perhaps most interestingly, Cook pointed to the iPhone battery program as another reasoning for the slowdown in iPhone sales:

We’ve started a program worldwide where we dramatically lower the battery replacement price. We had sort of a collection of items going on, some that are macroeconomic, some that are Apple-specific. We’re not going to sit around waiting for the macro to change. I hope that it does, and I’m actually optimistic, but we’re going to focus deeply on the things we can control.

Back in February on Apple’s Q1 2018 earnings call, Cook was asked whether or not the battery program could affect iPhone upgrades:

We did not consider what the battery program would do for upgrade rates. Sitting here now, I don’t know how it will impact upgrades. We did it because we saw it as the right thing to do for our customers. The effect on upgrades was not in our thought process in deciding what to do.

Elsewhere during the interview, Cook addressed Apple’s decision to stop reporting unit sales for the iPhone, iPad, and Mac – an announcement the company initially made last quarter.

The Apple CEO explained that, in Apple’s eyes, there is little reason to report unit sales because of the vast difference in price between various iPhone models. Cook pointed to the Apple Watch as an initial example of this, explaining that Apple never reported Watch unit sales due to varying prices between the different models of the device.

This doesn’t mean we’re never going to comment on units again. If we think we can better explain results with talking about units, I’d be glad to say something about it. But generally, to have it on a 90 day clock, I think it does the investor a disservice.

Lastly, Cook noted that Apple will start reporting the gross margin of its Services business:

We are making additional disclosures as well. For example, we’re going to give the gross margin of our Services business. We’ve never done that before. Services has grown an incredibly amount, we’re going to report over $10.8 billion for last quarter.