The battery has been in use for about 1 year. With the FIT Range Extender, including the Flyer attachment, the range between two charges can be significantly increased. Any retrofitting must be clarified with the bike dealer. In order for both batteries to be charged simultaneously in the e-bike (multibattery with range extender), a charger with software version V0.6.6.0 or higher must be used. The software version of the charger can be seen on the e-bike: Connect the charger, navigate to the left with the joystick of the control unit until the version is displayed in the top line of the display. A software update of the charger can be performed by the Flyer dealer. For more information, visit the following link: [hidden]