MacBook Pro Battery draining
My Mac Book Pro's battery is draining when it is shut down?
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If the laptop is completely shutdown, then the battery will slowly drain over time, but it should take a while and should not be noticeable over the short term. Power is always being used to check for the power button being pressed or to detect the lid being opened. Plus a battery will slowly discharge even if the battery was disconnected from the system.
If the battery is draining quickly when "shutdown", then perhaps the laptop never completed the shutdown process. It is surprising how long it can take for the shutdown process to finish. Try pressing the Caps lock key before shutting down the laptop. Usually the caps lock LED goes out at the end of the shutdown process.
Option click the battery icon on the menu bar and check the battery status. If the status is anything but "Normal" or "Good", then the battery has a problem. You can also run the Apple Hardware Test or Apple Diagnostics depending on the age of the laptop.