With all the fuss surrounding Apple's admission that it does throttle older phones, it was something of a relief to hear that the problem could be fixed by replacing the battery and that Apple would be lowering the cost of said replacement to £25. There is a catch, though, since you can only claim that discounted replacement once per device.
At the moment Apple is willing to replace the battery of any eligible device (iPhone 6 or newer) regardless of whether it fails a diagnostic test or not. MacRumours noticed there was a minor catch involved, though, with Apple's service pricing page stating this was a one time deal. An iPhone is only eligible for one no-questions asked discounted battery replacement.
Obviously if you have two iPhones you can go ahead and get both batteries replaced, but don't go trying to abuse the system by getting a replacement for your replacement. The offer is open until 31st December this year, so clearly Apple is trying to avoid people abusing the system. You know someone out there had hoped they could get a cheap replacement now, then get it done again in December to bring their phone back to near-perfect shape.
The good news is that this limit only applies to people with phones that pass the diagnostic tests. If any phones do fail between now and the end of the year, Apple will still honour that discount - even if you've already had your cheap replacement. Presumably Apple has more than enough confidence in its batteries to assume such cases will be rare. [MacRumours via Ubergizmo]