Further Details:
Regular alkaline batteries:
These used to be hazardous due to mercury content. Mercury, if released into the environment, can contaminate lakes and streams, the plants and animals who live there, and eventually people who eat the fish. In 1996, Congress enacted the "Battery Act," which among other things banned the use of mercury in these batteries. The State of NH beat them to the punch by enacting similar legislation in 1995 for batteries sold in NH. So what it comes down to is that batteries manufactured and sold before 1995 or 1996 probably have mercury in them and should be taken to a household hazardous waste (HHW) collection event. Those made after that can simply be tossed into the trash. One exception to the "new is safe" rule is foreign batteries--U.S. law has no bearing on what Japan or other nations might put in their batteries, so you may want to bring those to an HHW collection.
Please Note: No batteries should be thrown into trash which will be incinerated due to the potential for heavy metals going up the stack. Most municipalities which incinerate their trash have an active battery recycling program. Trash from GUVSWD residents is sent to a landfill, not incinerated, that is why we recommend trashing them here. Plymouth, Windsor, Springfield, Westminster, and towns in between send their trash to an incinerator, so please recycle batteries if you live there.
Rechargeable Batteries:
All rechargeable batteries seem to have something in them that makes them hazardous, and valuable as a recyclable, usually heavy metals. Therefore, all rechargeable batteries should be recycled or taken to a HHW event. The most popular rechargeable batteries are Nickel-Cadmium, known as Ni-Cd (pronounced nie'-cad). Another common type is Nickel-Metal Hydride (Ni-MH). Rechargeables are used for power tools, cell phones, laptops, flashlights, and many other household items. Most retailers that sell rechargeables also take old ones back free of charge and send them to a not-for-profit group called the Rechargeable Battery Recycling Corporation (http://www.rbrc.org) who reclaims the metals in them. They can also be taken to HHW events.
Button Batteries:
Button batteries are found in small items such as hearing aids, watches, and toys and are about the size of--you guessed it--a button. Button batteries can be alkaline, silver, mercury-oxide, or other cell-type. It is best to take any button batteries to an HHW event for collection as all of them contain some sort of hazardous material. Alkaline button batteries contain mercury even though their larger cousins do not.
Auto Batteries:
Car batteries are known as "wet-cell" lead-acid as they contain liquid sulfuric acid. Due to both the acid and the lead, car batteries are considered hazardous. Yet because they contain so much lead which is easily reclaimed, they have value.
Auto parts stores sometimes give rebates on new batteries when you bring in your old one. Or take it to a metal recycler, recycling center that takes them (e.g. "Hartford Recycling Center"), or to a hazardous waste collection.