This 2.5 amp hour rapid charger is designed for Vexilar Lithium batteries ONLY and works best when connected directly to the battery terminals using the supplied Gator clips. As the RAPID name implies, it is the best choice for many of the higher amp 12 volt batteries that you need to get a charge into quickly. The easy to understand charging lights make charging a snap. Green light signals power or charge complete. Red light tells you the battery is charging. Blinking red is a warning that the battery is too cold to charge or the terminals are reversed.