The statement that "for safety, battery charger leads must be connected to the battery after the charger is turned on" is False.
Why the statement is false
The statement is false because connecting leads while the charger is on would likely lead to a risk of sparking, and this could ignite flammable materials and cause a fire. Additionally, connecting the leads while the charger is on can destroy the battery thus causing a change to a new one.
To safely connect the charger, turn it off, and connect the red positive clamp to the red terminal and the black to the negative terminal. Plug the charger in some outlet and turn it on.