I have seen this question asked in previous seasons, but the question never specifically mentions a power source that comes with an item, so I assume you may say it’s not legal due to the fact that the batteries may be used improperly or poorly fabricated by the students.
If I have some LED lights (more specifically EL wire) that come with a battery pack would this be legal? this would be a self contained power supply which should be as safe as what you would find in a small video camera. This is the same type of wire used by the drummers in the Saturday morning show at Worlds this year.