The iTunes description says, “Ever wondered why your battery is draining so quickly? Just install Carat, open it every few days so it can send data to our servers, and within a week Carat will start recommending Actions (just for you!) and even predicting the improvements you will see. Although Carat cannot measure energy use directly, it infers what apps are responsible using advanced machine learning methods. Carat will tell you which apps it thinks are hogs (they use a lot of battery) and which are bugs (they use a lot of battery on your device but not most others). Being a hog or a bug does not make an app ‘bad’, but a user trying to improve their battery life can use these designations to adjust their behavior.”
Since Apple doesn’t offer too much information about the apps in the App Store, what Carat does is mainly based on simple assumptions that could be inaccurate.
After Carat gathers enough information about the device, it starts offering advices about what apps that consume excessive energy can be closed.
For each tip, users also get an estimate on the potential increase in battery life.