What do the different charge rate settings (Charge, Boost, and Engine Start) do?

The Charge setting is for charging small and large batteries at a standard rate. The Boost setting quickly adds energy to a severely discharged or large capacity battery prior to Engine Start. The Engine Start setting provides additional amps for cranking an engine with a weak or run-down battery and should always be used in combination with a battery. Using Engine Start without a battery installed could damage the vehicle's electrical system.