Rechargeable 3.6 Volt 900 Mah NiCad Battery with 21REC Connector --- Chemistry: Nickel Cadmium (Nicad) Dimensions: 0.57" Diameter x 5.68" High Configuration: Three Cells in a Vertical Stack Connector: 21REC   BatteryGuy Nicad Batteries Typically Have 20% - 40% More Capacity Than Other Regularly Available Batteries of the Same Size and Can Support up to 500 Charge/ Discharge Cycles or Five Years Standby Power Under Normal Conditions.  Nickel Cadmium Batteries Are Commonly Found in Emergency Lighting, Alarm/ Security Systems, Backup Power Devices and Other Electrical Devices.