Capacitors won't hold a charge indefinitely; as time goes on, charge gradually migrates from the positive to the negative plate. We can model this as a discharge of the capacitor through an internal "leakage resistance." A 0.30 F capacitor charged to 2.8 V will initially discharge with a leakage current of 0.30 mA.
What is the leakage resistant?
How long will it take for the capacitor voltage to drop to 1.0 V?