I shut down my brand-new laptop last night when the battery was around 80%. It wasn't connected to the charger, and I expected it to remain off overnight. This morning it showed only 5% battery. I later noticed that it had powered on around 3 a.m. and downloaded and installed several Windows updates. What could have caused this, and how can I prevent it from happening again?
4 Answers
Make sure you’re selecting Start > Power > Shut down rather than simply closing the lid or pressing the power button. You can also hold Shift while clicking Shut down to force a more complete shutdown. If you want the lid to turn the laptop off, change the lid-close action from Sleep to Shut down or Hibernate.
Since the laptop is new and it reportedly turned on around 3 a.m. to install updates, a worn-out battery is unlikely to be the main cause. First confirm that it is truly shutting down and review the Windows sleep and update settings. If it still loses a large amount of charge while fully powered off, then check battery health and contact the manufacturer.
Look in the BIOS or firmware settings for options such as USB power while off, wake-on-LAN, wake timers, or Modern Standby. Disabling those can prevent the laptop from waking or powering accessories when it should be off. Enabling the platform’s deep power-saving or ErP setting may help too, although the exact name depends on the manufacturer.
Windows laptops can appear to be shut down while actually using a low-power sleep mode, especially with Modern Standby or Fast Startup enabled. The computer may also wake itself for updates, then remain active or get stuck during the process. Check your power settings and consider disabling Fast Startup and wake timers.

Also check whether Windows is configured to install updates overnight. An update can wake the machine after shutdown and leave it running long enough to drain the battery.