Hi mohiniss!
What kind of battery charger do you need, or, to be more precise, what kind of batteries are you planning to charge with it? NiCd? NiMH? LiIon? car battery (lead-acid)? Or something other? Next...does it has to be an "intelligent charger" or just a plain one?
There are loads of battery chargers circuits on the Internet.
Go to google and do a search on "battery +charger +schematic" and "battery +charger +circuit" (without the quotes, of course).
I'm sure you'll find what you need.