Battery capacity diminishes over time, which is why iPhones and iPads last for less time on one charge as the years roll by. If you think your iPhone’s battery is suffering from this malaise, a Genius at the Apple Store uses a special technique to load a testing app onto your device to get the raw data. Without jailbreaking, that used to be the only option to discover this information. Well, until now, that is.
Battery Life can apparently show your battery’s original capacity alongside its current capacity (which will always be less unless your phone is brand new).
We suspect Battery Life is one of those apps that access non-authorized APIs, and that perhaps shouldn’t have made it through the App Store vetting processes. We’d advise you to download it now rather than later in case it gets removed. It’s free for the basic (and most useful) functionality.
To view the raw data, tap the menu icon at the top left, and select the entry in the list.
As for what’s healthy, or not, Battery Life informs you via a percentage figure and color-coded bar graph line. Anything less than 80% is usually considered sub-optimal, and at the stage where the battery might be replaced. If you want to get the most battery life from your battery then check what apps are eating it up (Settings app > Battery), and also keep your screen backlighting as low as you can (perhaps turning off Auto-Brightness – Settings app > Display & Brightness).