I’ve done it a few times with the 160wh range extender on a trek fuel exe
There were no issues. Have flown with easyjet and Ryanair, no pre authorisation was required.
Have taken it through Manchester, malaga, and Geneva airports
The range extender needs to go in your hand baggage, if there are any exposed terminals they needs to be taped over with insulation tape.
Once (at Manchester Airport) I was asked what it was, I told them it was a battery for an ebike and they just sent me on my way. Every other time it’s just gone through the scanners with no questions asked.