The Energizer Pro Charger integrates sound into the process of charging your batteries. A series of beeps will play to indicate that the charging has initiated and another series of beeps will play when the batteries are fully charged. This will ensure your batteries are fully charged every time which will help maximize battery performance. Additionally there is another sound that plays to indicate when a battery has expired and can no longer be charged. The Energizer Pro Charger comes with 4-AA Energizer Universal NiMH Rechargeable batteries (1400 mAh). Energizer Universal Rechargeable batteries have up to a 5 year lifespan and can be charged up to 1500 times. Energizer's AA products are now infused with extended-life additives to provide consumers with a usable battery life of 5 years.