The main aim of this paper is to provide an uninterruptable, stable and reliable power supply with the help of battery charger and battery bank which can be used for the operation of the switchgear and protection devices in the substations. Each feeder in the power system has its own protection devices that protect the power system from unwanted faults. Therefore, which require uninterruptible DC auxiliary supply to function. In order to operate these devices, the Float Cum Boost Charger (FCBC) is analyzed which both converts the AC power to the DC power to feed the auxiliary power supply and also charges the battery bank to store the energy and inject it into the system when it needed. It provides 100% no-break supply to the critical loads. The main parameters to be considered are, the capacity of the battery bank, the type of battery, supplying enough power to operate the protection devices, the charging time of all the batteries, etc.