The company recently launched a $29 battery replacement program after admitting that it been secretly slowing down devices as their batteries aged.
"While this is a good PR move for Apple to resolve the issue, we are concerned it could be a mild headwind for iPhone unit sales if more iPhone users decide to take the offer instead of upgrading to a new device," Barclays said.
It's estimated that 77% of iPhone users are eligible to upgrade their battery.
"In our base case scenario, 10% of those 519M users take the $29 offer, and around 30% of them decide not to buy a new iPhone this year. This means around 16M iPhone sales could be at risk, creating ~4% downside to our current revenue estimate for C2018."
Barclays is neutral on AAPL and believes that Wall Street is "too optimistic about the iPhone X super cycle"; however, it notes that the new tax law and Apple's growth in services are positives.