Nowadays, batteries have a wide application due to usage as a power provider in electrical and electronic systems and as an energy supplier in many energy generation systems. Thus, investigation of challenges related to batteries is important. Because of limitation in battery cell capacity and voltage and for achieving higher capacity and voltage, series and parallel combination is used. Battery systems would be created with cells combination. In a battery system balancing of charge between system cells whether in charging or discharging time is one of most importance issues. Since balancing of charge in battery cells increases battery life and operation reliability of a battery system various methods for cell balancing have been proposed. These methods divide into two groups: dissipative and non-dissipative. In this thesis, first methods are investigated and their advantages and disadvantages are noticed. In one group of proposed methods dc-dc converters are used for cell balancing and it is showed that usage of these converters increases system operation reliability. But hard switching in these converters causes the increase in dissipations and noise and leads to magnetics interferences in system. For this reason soft switching converters using is considered. A branch of soft switching converters are resonant converters which in them switching operates in soft condition without the need for an auxiliary circuit. SwRC family converters have this property too. Then in this thesis, a buck-boost converter is proposed with change in buck-G SwRC converter circuit topology. All active elements of proposed converter are in soft condition. Analyzing operational modes with main waves diagram, step by step design method with examples and simulation and implementation converter results for performance validation of proposed converter are provided. A cell balancing method based on proposed converter is presented and all operational situations of proposed method with circuit schematic diagram are provided. Also to illustrate the matter simulation results and implementation results for a balancer which has three Li-ion cells are provided. Comparison of analytical, simulation and implementation results shows a good agreement between them. In addition to decrease in dissipations the proposed method because of switching in soft situation, has less elements and complexity than similar methods and leads to increase in cell balancing speed. Keywords: 1- Battery 2- Cell balancing 3- dc-dc converters 4- soft switching converters