There is a thread which might help you out
here
Or the most basic charger is connecting 3 or 4 cells straight to your charge pad (after disconecting from the controller).
But there are many different ways depending on what you want. If you are building anysort of charger make sure you have a multimeter so as to test the current you are pushing into the car batt. And never let your car batt get too hot to touch.