I packed it in this bag that @braswell recommended.
It was the perfect fit. I added some bubble wrap for the international flight.
The flight out of Seattle to SFO was uneventful. No questions asked.
For the flight from SFO to Manila, I asked the lady at the check-in counter if she could put a fragile sticker on it. She then asked me to disclose what was in it.
I told her that it was an electric skateboard. She then had to call a supervisor to see if it was okay.
I told them it was discharged and was safe to fly. It was then allowed on the flight.
In retrospect, I feel I should not have asked for a fragile sticker and brought attention to the bag.
The local flight from Manila to Misibis Bay, was also uneventful.
I'll let you know if any of the flights back have any issues.