FILE PHOTO: Apple CEO Tim Cook stands in front of a screen displaying the IPhone 6 during a presentation at Apple headquarters in Cupertino, California October 16, 2014. REUTERS/Robert Galbraith/File Photo

(Reuters) - Apple Inc's AAPL.O offer to replace flagging batteries at a slashed rate could be a hurdle for iPhone unit sales in 2018 if more users take the deal over upgrading to a new device, Barclays analysts write in a note.

Apple’s customers have not been very pleased since the company said last month it intentionally slowed down older iPhones with weakening batteries to prevent the handset from shutting off abruptly.

Following consumer outrage, Apple apologized and slashed the price of out-of-warranty replacement batteries to $29 from $79 for iPhone 6 or later models.

Barclays analyst Mark Moskowitz says 77 percent of iPhone customers are using iPhone 6, 6 Plus, 6s, 6s Plus, 7, 7 Plus, and SE, which means even a small percentage opting for battery replacement over upgrade could have meaningful impact on iPhone sales.

The company faces eight lawsuits filed in California, New York and Illinois over the issue.