DC-DC converter is widely developed due to its simpler form and higher efficiency. There are two types of converters namely buck and boost. Buck is used to lower the voltage and boost to increase the voltage. Buck-boost converter PWM settings will increase efficiency when charging batteries (batteries) Buck-Boost Converter built-in charging system aims to test the capabilities of the Buck-Boost Converter by knowing the efficiency and long-term value of the Buck-Boost Converter for the battery charging system, as well as knowing the changes in input and output voltage from Buck -Boost Converter for PWM value change provided. From previous research it shows that Buck-Boost Converter can accept input voltage of 8V s.d. 24V produces 3V output voltage.d. 41.6V supplied with PWM. The capabilities of the Buck-Boost Converter series deliver the highest efficiency of 94%. The Buck-Boost Converter for the battery charging system uses an output voltage set of 13V at an initial condition of 11.96V to 12.8V within 60 minutes, and a second test with an initial condition of 8.69V to 12.6V within 120 minutes.