Hello GoldenWood909,
I am Jaspreet Singh.
Acer laptops have something called power off charging which essentially allows users to charge their devices through a USB port on the laptops even when the laptop is fully turned off.
If your laptop has a similar feature then an external hard drive or a mouse/controller will drain the battery even if it is turned off.
A better way to check it will be to measure the drain when no devices are plugged in.
Secondly try pressing down on power button until the system shown down. After a desired amount of time turn it on and see if the battery has still drained ( this will help us know if this is a hardware issue or software )