Why is Sleep eating so much battery? What about battery overheating?

Usually the battery consumption issue or related issues that cause the phone to overheat during sleep tracking are not directly caused by sleep tracking.

In most cases, sleep tracking itself does not consume too much battery (usually around 1-2% per hour of tracking). But because we keep a wake lock (keeping the phone awake), any other apps and processes can access the CPU extensively during the sleep tracking time. We would suggest checking what services are running before you go to sleep. Also, battery statistics are not a clue here, as all battery consumption goes to the app holding the wake lock, even if it did not consume the battery (this is by design in Android). This is hard for us to debug.
A good test would be to restart your phone (or kill any unnecessary services running) before using Sleep as Android and see if Sleep as Android still uses too much battery after that. One of the features of Sleep as Android that may cause higher CPU load during tracking is the noise recording. You can try tracking without it as a reference. We also strongly recommend tracking with airplane mode enabled.