Can you use Max Potion on a Pokemon with Energies attached but no damage on it?
No, you cannot. If you don't have any damage, you cannot use Max Potion on that Pokemon.
Source: TPCi Rules Team (2012-02-16)
Can you use Max Potion to heal a Pokemon that doesn't have any energy attached to it?
Yes, you can.
Source: Emerging Powers FAQ (2011-09-01), PUI Rules Team (2011-09-01)