Fully discharged cells take constant current charges at a rate of 1C (1x the rated capacity), until reaching their set voltage of between 3.6 and 4.2 volts (depending on specific chemistry), a process which takes approximately one hour. The batteries’ chargers then switch to constant voltage, with the current tapering off until the batteries are fully charged—approximately another two hours. The entire charging process is a fairly fast one, at about three hours.