The best way to stop your charger from overheating is to buy a quality charger in the first place. The best chargers on the market have in-built safety systems that prevent them from overheating and have temperature controls that match them to their climate. A lot of marine battery chargers have microprocessors installed that can read what your battery needs. These battery chargers also detect when a battery is fully charged and switch from a full charging mode, also known as bulk charging, to float charge mode, which safely finishes off the battery's charging process.