Buck-Boost charger, based on the buck-boost architecture, is able to stably manage the charging of batteries with different number of strings even under a wide range of input voltages, regardless of whether the input is lower or higher than the output. Buck-boost charger controller can be used with peripheral power tubes to realize high-power, high-precision and high-efficiency applications. Buck-boost charger converter, by integrating ultra-low Rdson power MOS, realizes a high-efficiency and small-size charging solution.