I have done this before, but I did have a problem.
FIRST- In Europe you can rent ebike batteries. Take your fave bike there and rent a battery for your time. Rare to find battery rental in the USA.
NEXT- My story. I had read of others taking their bikes with them on flights, so I thought I would do it too. Bike was boxed. It was accepted, but the girl at the counter had to do some digging and finally gave the OK for my battery to be carry on. TSA had no problem. They waved their magic wand over it and sent me on my way. Great.
However when it was time to go back, the Mexican boss at the airport wouldnt let me return with it. He called the CARGO guy who, of course, said it wasnt allowed. The logic of my argument that of course it was allowed, I brought it here on the plane!!
It was left behind with a friend. Arrgh! American Airlines said screw you too!
SO it can be done, but its not mainstream enough to be done reliably.