Nikon Quick Charger MH-21 is required to recharge the Lithium Ion battery ENEL-4 and EN-EL4a. The MH-21 is equipped with a battery calibration feature and charge lamp that glows, blink or turn off according to the battery charge state. The approximate charging time for a fully discharged ENEL-4/EN-EL4a is approximately 100 mins.
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