The original alternator program used to be 14.4V/28.8V as long as the engine was running and manufacturers have developed charge programs to reduce energy and hence fuel wastage. Different vehicle manufacturers use different charging profiles but even the same manufacturers continuously update their charge programs. The ELOGIC DC-DC battery charger are primarily intended to charge an auxiliary or service battery from a vehicle starter battery. The input battery voltage can be above, below or equal to the output battery voltage. So the ELOGIC DC-DC battery charger allows the auxiliary battery to be perfectly charged regardless of the input voltage, while being protected against damage due to peak voltages.