Apple has apologised for slowing down older iPhones and cut the price of battery replacements, although claimed it has "never – and would never – do anything to intentionally shorten" the life of its products.

The tech giant is facing a number of legal challenges since last week revealing that a software update slows down the iPhone 6, 6s, 7 and SE models when their batteries wear down over time.

In a letter on Thursday evening, Apple said it was aware some of its customers "feel Apple has let you down" and apologised.

Users have long suspected that ­Apple slows down older ­iPhones, but the company admitted it last week when a tester found performance slowing down when a battery degrades. While Apple says it does this to make the phones last longer, consumers have claimed it is a tactic to encourage ­upgrades, and have criticised the company for not coming clean about it.

Apple said there had "been a lot of misunderstanding about this issue", in its letter, adding it had not been seeking to "degrade the user experience to drive customer upgrades".

Instead Apple claimed its batteries became "less effective" as they chemically aged and this reduced their ability to hold a charge. This could be affected by the time and number of times a battery had been charged as well as the temperature of the environment in which an iPhone is being charged.