Stop Act Of Connecting A/C Adapter From Starting Up Laptop?

Question

We have some new laptops that we turn off with the lid closed and store them plug them into AC power in a charging cart so they are always charged up in the morning.
(It's possible that these laptops could have been in hibernation mode rather than "off").
We are having a problem where when power is applied to charge the battery, some of the laptops often do an unwanted power up.  Since we have full disk encryption, the laptop boots to a preboot screen asking for user credentials before Windows will load.
 Since it is not booted up into Windows at this point, it never goes to sleep and just keeps running and getting hot.
It is not network related because I unplugged the network cable, power off the laptop and then plugged in the AC cable and I saw the CD ROM LED light start flashing which indicates it powered back up.  I open the lid and see it powered up and was at
the encryption prompt again.
If I press and hold the power button to power it off again, it usually does not happen again, but I cannot rely on it. Random and unreliable.  Sometimes I have to power it off twice before I can plug it in without it powering up again.
There is a setting in the BIOS that enables the laptop powering up when power is applied, but I checked it and that setting is NOT enabled and, if it were, it should power up every time the power is applied instead of sporadically.
Obviously, it is not wake on LAN magic packets since it can happen even when the network cable is unplugged
Are there any other settings that can be configured to make sure the laptop stays off when powered of even if the external power is removed and re-added?
The cart cannot charge all the laptops simultaneously because of power limitations of a single 110V power outlet.
It charges groups of laptops for 30 minutes, then moves to another group for 30 minutes and keeps rotating until all the laptops are charged.  This means power is applied and reapplied all through the night and we don't want these laptops to keep waking
up and running on battery when the power is cycled off because it is wasting charge cycles on the batteries.

Answer 1

Hi,
Apologize for the late reply.
Please see if those two options could be the reason here:
1. A hardware might keep your computer awake. Usually this is caused by USB flash drives and USB mice.
2. A program or scheduled task might be waking your computer. By default, Power Option settings do not allow scheduled tasks to wake the computer from sleep or hibernate. However, some programs might awaken the computer if these settings have been changed.
For the steps to disable some hardware/application to interrupt the hibernation/sleep, please take a check in the
Why does my computer not go into sleep or hibernation as expected, or why does it wake unexpectedly?
part in the below article:
http://windows.microsoft.com/en-hk/windows7/sleep-and-hibernation-frequently-asked-questions
For more information about power management, please see if the following articles could help:
Power Management in Windows 7  and Troubleshoot Power Management Settings in Windows
7 .
Best regards
Michael Shao
TechNet Community Support