By adding Batteroo ReBoost battery sleeves to rechargeable batteries you can make the batteries work well with the devices that only support alkaline, and the sleeves improve the performance of the battery.The Batteroo ReBoost is an innovative and practical battery sleeve series that contains two models: SmartSleeve and SmartShell. As we can see from the images, the SmartSleeve features an ultra-thin and firm-fitting design that allows it to work with AAA, AA, C and D regular rechargeable batteries and fit in your devices.The SmartShell is an innovative battery adapter that allows you to use your AA/AAA rechargeable batteries in C/DBy adding Batteroo ReBoost battery sleeves to rechargeable batteries you can make the batteries work well with the devices that only support alkaline, and the sleeves improve the performance of the battery.The Batteroo ReBoost is an innovative and practical battery sleeve series that contains two models: SmartSleeve and SmartShell. As we can see from the images, the SmartSleeve features an ultra-thin and firm-fitting design that allows it to work with AAA, AA, C and D regular rechargeable batteries and fit in your devices.The SmartShell is an innovative battery adapter that allows you to use your AA/AAA rechargeable batteries in C/D