I rather missed the fact he was wanting a charger, and not a PSU - having already built a linear regulator confused me!.
You don't need a regulated supply for a charger, as TheOne always said, a thyristor charger is all you need - there are plenty of suitable designs all over the net.
If all you are looking for is a crude charger, which you need to manually look after and turn off to avoid overcharging, all you need is a transformer, a rectifier, and a current limiting resistor (a very BIG (high wattage) one. This is all that standard battery chargers contain - often they don't even have a resistor at all, the transformer is designed to give the current limiting.