I had this with a pair of Sony's first gen wireless earbuds, where the battery significantly began degrading just after year 1.
If I'd have raised this with them during year 1, John Lewis would have simply swapped them out with a new retail boxed set from the shelf; they did this for me with a pair of Bose headphones that developed a fault a few months in.
The authorised repairer for the Sony earbuds ended up replacing the earbuds with new units, but did not replace the charging case. The repair bill came to significantly more than what it would have cost John Lewis to have simply issued me with a new pair! The repair also took so long (some 9 weeks) that they also ended up giving me £50 in gift cards as compensation! Ended up selling them straight after to CEX...