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 0.37F capacitor charged to 3.9V will initially discharge with a leakage current of 0.30mA
What is the leakage resistance?
How long will it take for the capacitor voltage to drop to 1.0 V?