It is inter alia disclosed an apparatus (10), comprising a power connector (210) configured to be connected to a removable first rechargeable energy source and configured to supply power from the first rechargeable energy source to the apparatus via a power supply line (220), a second rechargeable energy source (240), a balancing element (230) placed between the power supply line (220) and the second rechargeable energy source (240) and configured to provide power from the power supply line (220) to the second rechargeable energy in a first state of the apparatus and configured to provide power from the second rechargeable energy source (240) to the power supply line (220) in a second state of the apparatus, wherein in the first state the apparatus is configured to prevent supplying power from the second rechargeable power supply (240) to the power supply line (220).