I rarely shut down my iPad 3: I leave it in sleep mode for many hours, often for many days. In my case, the battery drain during sleep is minimal (4G and location services are disabled) but I have some doubts:
- Could the iPad wake up from sleep without my intervention, for example because of a notification?
Yup. But the screen won't stay on for long, a few seconds at most.
- Is the wi-fi active in sleep mode?
Yup, that's how it gets notifications while in sleep. Sometimes, even if WiFi or Cellular is turned off, you'll get notifications. Some apps will send you a reminder from the app itself instead from a Push Notification Server (I think).
- What are the apps or services that could drain battery in sleep mode?
Navigation is one. Anything you leave active when you put it to sleep will continue to run. If you exit to the home screen prior to sleep, the apps will only run for ten minutes before stopping. Otherwise the app open when you sleep will run constantly, such as navigation.
- Is it safe to leave the iPad (in sleep mode) into a shut tight sleeve case? I fear it could somehow get warm also in sleep mode.
There's no issue under most circumstances. Most apps stop all major CPU usage when the iPad sleeps so the iPad won't get warm unless the sleeve is in the Sun or the environment is hot.
