When a capacitor is connected to a battery, charge is rapidly conducted off of one plate, through the battery, and onto the other plate, until the potential difference across the capacitor equals the potential difference across the battery.
If the circuit includes a resistor, the process of charging is slowed down (the greater the resistance, the more time it takes).
It can be shown that the product of the resistance and the capacitance (R∙C) represents a "time constant" (τ) that is equal to the time it takes for either one of the capacitor plates to reach 63% of its maximum charge. (It takes an infinite amount of time to fully charge).
