In order to work properly, the battery has to be maintained e.g. after a long winter pause. This is done by the battery conditioner. By automatically charging and discharging it simulates the day-to-day operation. Due to this cyclical, battery preserving alternation of charge and discharge the battery stays fresh, this counteracts the aging process. The compact unit is suitable for all rechargeable 12 volt lead batteries with a capacity of 10 to 150 ah. In addition the battery conditioner is able to temporarily replace a battery when used as a backup power supply. If a battery of a vehicle has to be removed or replaced, the battery conditioner takes over feeding the consumer load. Thus stored data like for car hifi systems for instance is preserved. Dimensions W 7 x H 6 x D 10 cm, weight 450 g.