works or other rechargeable batteries are not compatible

Excellent product. Tested with a voltmeter: 1.37 against 1.25 volts for most rechargeable batteries. Why do these technical details? Some devices do not work with rechargeable batteries because they require more voltage (1.50 volt) rechargeable batteries are often too low but not the Varta who with 1.37 volts, approach alkaline batteries. And all this refilled. I'm glad. A product also perfect for camera (flash).