An electrical system includes a battery for providing electrical power to a starter mechanism and an auxiliary load of a hybrid-electric vehicle. An electric double-layer capacitor (“EDLC”) is electrically connectable to the battery and the auxiliary load. A separation switch is electrically connected between the battery and the EDLC for electrically separating the battery from the EDLC and the auxiliary load. The separation switch is opened in response to the voltage across the battery being less than the voltage across the EDLC.