Common household batteries are also called alkaline batteries; the chemical type is important in choosing proper disposal options.
While “regular” batteries - AA, AAA, C, D, 9-volt - contained high levels of mercury until approximately 1997, today’s contain just trace elements of toxins. They are no longer considered a threat to properly equipped modern landfills. Dispose of standard alkaline batteries in the regular trash.
Rechargeable Lithium batteries are considered Household Hazardous Waste and must be disposed of accordingly.
When disposing of 9-volt batteries, always tape over the terminals with masking, duct, or electrical tape. Because both terminals are on the same end of the battery, even a “dead” 9-volt has enough power to spark a fire!
After the positive and negative posts are securely taped, 9-volt batteries can be disposed of in your regular trash. Read more about 9-volt battery safety (PDF).