According to some reports, your electronic devices are checked whether they turn on before you can get on a US bound flight. What if I carry around a laptop without a battery?
not ARE, but CAN BE. If asked and you can't turn it on, it can be confiscated.
No reason to risk it, just charge the darn thing before you leave and have the battery in.
Only devices in carry-on luggage are checked. If you for some reason need to take laptop w/o battery or with battery discharged, you can still put it in the checked-in luggage.
Why do they want to check that electronic devices turn on? Because it is possible to create explosives that very much look like a battery when they are x-rayed. So to make sure that your laptop doesn't contain explosives, they ask you to turn it on.
If you have no battery, then obviously you don't have any explosives pretending to be a battery either. So they should not require you to turn the laptop on, or opening the battery case and showing there is no battery should be fine as well. So if the security people can think logically, you will be fine.
But would you want to bet that they can think logically?
PS. Googled and found an article from 2014 claiming that British Airways won't let you on a flight if you have a device that doesn't turn on - even if you manage to charge the device and come back. Which is utterly ridiculous but not unexpected.