Buck-Boost DC-DC Converter 25A The DC-DC converter is used to charge a 12V/24V service battery in vehicles with an intelligent alternator. The Buck-Boost DC-DC converter is crucial because the alternators operated by the onboard electronics of Euro 5 and 6 engines do not always provide the correct charging current. A DC-DC converter is necessary to properly charge the service battery. Additionally, it is almost essential to use a booster when charging a lithium battery. Lithium batteries have a very low internal resistance and draw as much current as the alternator provides. This can lead to overloading the alternator and/or the wiring. A booster limits this current. Only with the Buck-Boost can the charging current be freely adjusted.