Make most if not all rings chargeable:

• Hunger / slow digestion: merge, and the positive and negative enchantment work different ways.
• Stealth works in a radius / makes monsters have to roll higher to detect you.
• Warning increases or decreases its regular radius.
• Aggravate monster works in a radius, or affects monsters’ rolls for being aggravated.
• Invisibility / see invisible: work in a radius, possibly.
• Searching: radius or have it affect your chance of finding something
• Polymorph / teleportation: affect the frequency at which it triggers
• Conflict: radius or affect monster rolls
• Most other rings that confer binary trinsics like teleport control or free action or sustain ability are difficult to make chargeable.