Some iPhone owners who jumped on the replacement program during its initial weekend had been denied fresh batteries, since their power packs were otherwise healthy. They shouldn't have a problem throughout the rest of the discount period, which ends in December.

The no-strings-attached gesture is clearly part of Apple's mea culpa: you can get a fresh power pack if you're even slightly worried. At the same time, it's also helpful if you know you tend to thrash batteries, or if you just want to wring out as much use as possible before you consider an upgrade.