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Apple started offering $29 in-store battery replacements last week in an apologetic move after the company revealed that an older battery could actually make an iPhone run slower.

It's a win for customers who can now extend the life of their iPhone at a lower price, increasing both its battery life and its performance.

But it may be bad for Apple's bottom line, analysts at Barclays wrote in a note on Wednesday.

"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," the analyst Mark Moskowitz and team wrote.

They model that as many as 16 million fewer iPhones could be sold in the coming year thanks to the offer. That comes out to as much as $10.29 billion in lost revenue, according to the Barclays model.