NOVELTY - The unit (200) has electric contact pads provided on an outer surface of the unit. A dynamically configurable connection unit electrically connects each positive and negative voltage supply terminals of an electric energy reservoir (222) to the electric contact pads, where electric energy is drawn from the energy reservoir through selectively different combinations of the electric contact pads. The dynamically configurable connection unit is programmable to connect each positive and negative voltage supply terminals to single respective electric contact pads at given time.    USE - Battery unit e.g. electric device, such as electric vehicle and shell for an external electronic device in a pumping application.    ADVANTAGE - The unit provides a resting state to prevent damaging of the energy reservoir when the cell voltage is low, which is monitored periodically. The unit allows a tank to include safety functions to prevent over-charging, over-discharging and shorting terminals so as to provide environmental protection for the units against dust, water and other contaminants. The tank provides and maintains a static overpressure in relation to the pressure caused by pure gravity between the units such that an additional static pressure is applied to the tank to increase normal forces between the contact areas of the units and contact surfaces of the tank after filling and potential agitation, so that normal forces is more uniform between different contacts, thus improving ability of the system to withstand vibration and shocks during the operation. The unit allows a connection unit to connect two contact areas electrically together to form a current bypass route from the contact area to other contact area, thus increasing tank programming possibilities. The unit allows the terminals of the energy reservoirs to be disconnected from the contact areas so as to avoid undesired or uncontrolled connections, shorts and sparks inside the tank in a cost-effective manner.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a battery unit in a general level.    Battery unit (200)    Contact areas (202a-202d)    Switching logic (220)    Electric energy reservoir (222)