Charges 2 or 4 AA or AAA at a time, checks if the batteries are still rechargeable. Fuel gauge and count-down clock tells when batteries are done charging. Maximizes cycle life of the NiMH cells with built in over charge protection. Shut-off mechanism: Delta volt detection, 5 hrs timer. Sound indicators, single beep/start, double/done. Three-stage status indicators: red, charging 0-49%, amber, charging (50-99%), green, fully charged. Bad battery detection alert, If a bad battery is detected a red x will illuminate; with repetitive audible beep. Folding plug, reverse polarity protection. Primary battery detection. Typical weight: 113.0 g (3.9 oz).