There are many reasons to recycle batteries rather than throwing them in the garbage but the most common is to avoid lead, corrosive acids and heavy metals contained in batteries from polluting the environment after these substances enter through groundwater, surface water or rain (source: http://www.brighthub.com/environment/green-living/articles/44363.aspx).
Recycling alkaline and rechargeable batteries is easier than ever, with many dropoff locations in every city.
Plug in your postal code at Call2Recycle to find the nearest locations for recycling batteries.
Don't forget to ask!
Many stores will accept their own store batteries for recycling. Some locations accept different types of items for recycling (i.e. car batteries, compact fluorescent bulbs) so you can recycle a bunch of items at one time.
Dropoff locations for other items can be found in the Recycling Council of British Columbia's recyclepedia.