If At First You Don’t Succeed … ?
Apple has a very interesting relationship with batteries, one which has not gone well for them in the past unless you consider legal action against your own policies a success. Not content with artificially slowing your phone as your battery ages, Apple is now blocking the ability to replace your iPhone battery on your own or with help from a third party.
Official Apple batteries have a TI microcontroller which holds the unique authentication key your phone wants before it will show you your battery health, so as of now a third party battery will only ever show the status ‘service’ and not the amount of charge left. Considering that The Inquirer has verified you can get an Apple Genius to use a software tool to authenticate a third party battery for you, it does not seem that this is a protective measure but instead an idea they picked up from a certain printer company.
However, the fiddlers at iFixit found that even if someone replaced their iPhone battery with one from another iPhone, they'd be greeted by a message in the Battery Health that simply declares 'Service', rather than reveal battery data such as how much the pack may have degraded and what it's maximum capacity is.