This 6 V battery charger was found on a 1987 Hands On Electronics. Rc determines the charging current and must be calculated according to the battery. The transistor Q1 must be equipped with a heatsink and the transformer secondary must have a current according to the maximum of the intended load. The necessary changes were made to make assembly possible with more current components. The diodes can also be 1N4002 and the transformer has a secondary current of 200 to 500 mA.