The energizer pro charger battery charger plus 4x aa 2000 mah can tell you when your rechargeable batteries will be fully charged so you can leave them to it how full your rechargeable batteries are via both visual and audible indicators if your rechargeable batteries can still receive a charge so you know when to replace them and when a non rechargeable or old battery is in the charger a red x instantly appears rrthe energizer pro charger charges four aa or aaa batteries in 3 to 5 hours