The invention relates to a battery charger comprising a primary circuit: a secondary circuit consisting of at least one transformer secondary and a rectifier; and an overload prevention circuit. According to the invention, the primary circuit is provided with at least one general switch (5), a switch (6b) that is actuated by a relay (6a) in accordance with determined load conditions and a transformer primary, all of which are disposed in series. The overload prevention circuit comprises a voltage-sensitive switch and at least one reactance (7, 7a, 7b, 7c, 7d) is disposed in the primary circuit or between the transformer and the rectifier in the secondary circuit. The invention is suitable for producing battery chargers.