Apple has the most thorough refurbishing process as far as I know. No matter what a device is returned to them for (even for open box), they give the device a new battery. They replace the software and diagnose/repair any hardware issues. All cosmetic damage is repaired, if possible, and then the device leaves the refurb factory in like new (basically new) condition. Far too many manufacturers only do half as much work on their refurbished devices.