The Duo Charger for EN-EL18- and EN-EL4-Series Rechargeable Batteries from Watson charges batteries in sequential order. Therefore, once the first battery is fully charged, it automatically switches to the second battery and starts the charging process over. The LEDs indicate what level your battery is at, and the charger protects them from short-circuiting and instantly shuts off if the batteries are overheating. Because of the switching power between 100 to 240 VAC, you are able to use the charger anywhere in the world. The DUO Charger is compatible with Nikon EN-EL18, EN-EL18a, EN-EL18b, and EN-EL18c type batteries, and adapter plates are included, so you can also charge EN-EL4 and EN-EL4a type batteries as well. Battery Compatibility With Built-In Bays: Nikon EN-EL18, EN-EL18a, EN-EL18b, and EN-EL18c. With Included adapter Plates: Nikon EN-EL4 and EN-EL4a. Battery Status LEDs indicate what level your battery is charged. Battery Protection The charger protects the batteries from short-circuiting and instantly shuts off if the batteries are overheating. Worldwide Usage Because of the switching power between 100 to 240 VAC, you are able use it anywhere in the world. Watson D-3416 Specs Charger AC Input Power: 100 to 240 VAC, 50 / 60 Hz at 980 mA Output Voltage: 0 to 12.6 VDC Number of Battery Bays: 2 Indicator: LED Operating Temperature: 32 to 104°F / 0 to 40°C Cable Length: 39.2" / 99.57 cm Dimensions (W x H x D): 2.0 x 6.3 x 3.4" / 50.8 x 160.0 x 86.4 mm Weight: 8 oz / 227 g Packaging Info Package Weight: 0.91 lb Box Dimensions (LxWxH): 6.8 x 6.1 x 2.4"