Abstract: In ships electricity is generated by the use of alternators. These alternators are equipped with an inbuilt rectifier which gives a DC output. Depending on the speed of the alternator the output voltage will be either 48-volts or 12-volts. Now the ship generally has two different batteries with 48-volts (housing battery’s) and 12-volts (Engine block battery’s). These batteries are responsible for providing power for both engine block and for housing purpose as well. This battery’s need to be charged. When the alternator is providing a output voltage of 48-volts the 48-volts will be directly charged and a buck convertor is used to step down the voltage from 48-volts to 12-volts and charge 12-volts battery’s. when the alternators are providing a voltage of 12-volts the 12-volt batteries are directly charged and if they charge fully the the boost convertor is used to step-up the voltage and charge the 48-volts battery. Depending on speed of the alternator the output voltage varies to defined values and based on these either boost or buck operation takes place.