I think he has willpower, but a fragile (compared to some heros) psyche that gives him some advantages (using his multiple identities to gather information, moving in different segments of society), but also makes him more prone to mental illness. So something like the Penance Stare might be a vulnerability.
The reason I think he has willpower is that he somehow always finds a way to win against the odds, even when he has been beat down first.
But, reading more about the Penance Stare I think it is not so likely that Batman will get close enough to use it. So my revised opinion is:
Moon Knight 8/10