A device for servicing/maintaining a high-voltage battery, which has individual battery cells or battery modules, and high-voltage positive and negative terminals, and a battery management system having a data transmission terminal for bidirectionally transmitting management system data between the management system and an information-processing unit, external to the battery. The device includes at least two of: a battery charge device, a battery discharge device, and a battery diagnostic device. A battery charge device brings a battery to a higher charge state, and has positive and negative terminals to be connected to positive and negative battery terminals. A battery diagnostic device checks a battery, and the device, for the presence of internal errors, and to indicate recognized internal errors, and may also produce diagnostic data for the battery state and triggering functions directed to bring the device and/or battery safely into a different state, to operate/test them.