Bidirectional flyback dc-dc converters are widely used for low power capacitive load charging. The performance of such converters are highly dependent on device parasitics which are mostly capacitive in nature. Implementation of soft switching methods like first resonant valley mode switching exploit their presence to minimize the device stress and loss. However in the process, these parasitic capacitances consume some energy supplied from the source. This trapped energy becomes significant at high operating voltage. In this paper a detailed analytical model of charging process of such converters has been established. The analytical model is used to show the role of parasitic capacitance in limiting the maximum achievable output voltage. A hardware prototype has been established based on optimal charging principles and experimental results obtained from it are also presented. © 2016 IEEE.