Upvote:2
If the battery doesn't work so you know you'll have to use the power cord anyway, could you remove the battery and leave it at home for your trip? I understood the issue to be that batteries were being used to conceal explosives, so if you don't have a battery at all that might be OK.
Upvote:3
I flew with Delta to the US last week. In the queue to the checkin counter (when they put those little stickers on the back of your passport) I was asked if all electronics where sufficiently charged to be able to demonstrate that they were working devices. However, at no point was I asked to actually do that.
My conclusion: you could be asked to power up the laptop but won't always. As far as I understood, what they mainly are concerned about is that you would replace the battery with explosives. For this reason I assume that powering up using the power cord will not be sufficient.
I was flying from Western Europe, but not the UK. I am not sure if this only applies to hand luggage or also to checked luggage.