At the security checkpoint you have to take a laptop out of your bag and put it through the scanner separately and they may ask you to turn it on to show it works (which generally will require the battery to be installed). So, whilst you should be able to, in order to prove the laptop is a laptop and not been gutted to create a bomb may require it to be powered up - and they may not allow you to plug into the mains to do so...
The battery to my laptop died after 1.5 years but I have been using the computer with a power supply. The battery is still connected to the laptop because I am afraid it will get dust inside?
I travel alot with my laptop and have never been asked to turn the computer on so far, but would security confiscate it if I could not boot it up using only the battery? This is, if they prohibit me from using a power socket for the power supply.
Also, the dead battery is always connected to the laptop and I never remove the power chord when going to sleep. Is this still dangerous, even if the battery is dead and not capable of charging?