I read somewhere that settlers will enter a Power Armour if you leave them around with the fusion core in them.
It sounds like great roleplaying to collect all the power armours found throughout the commonwealth and let an entire settlement run around in power armours.
But do they need to be supplied with new Fusion cores?
This question is similar to Do companions drain fusion cores? but not a duplicate as that question does not answer the behaviour of settlers, only companions which could be different. If that question is updated to include companions then I am happy to close this question.