Look at these links for some circuits:-
http://www.aaroncake.net/circuits/charger2.asp
http://www.discovercircuits.com/B/batt-chrg.htm
http://web-ee.com/schematics/battery_chargers/battery-charger/
http://www3.telus.net/chemelec/Projects/Car-Battery-Charger/Car-Battery-Charger.htm