An ultracapacitor-based power source includes an ultracapacitor, a charger, output connections and a power source controller. The ultracapacitor-based power source is suitable for backup starting of a starter powered by a starter battery. The charger charges the UC from an energy source. The output connections connect to the starter in parallel with the starter battery. When a start attempt failure occurs, the power source controller connects the UC to the outputs. The connection directs current flow from the UC to the starter, thereby starting the starter from the UC.