A system for providing an identification of a leakage current between a plurality of electrochemical battery cells (101, 102) connected in a series arrangement, each cell having a first cell terminal and a second cell terminal, wherein the system comprises cell connection circuitry and an apparatus configured to provide for the identification of the leakage current, wherein the cell connection circuitry comprises: a first cell connection terminal for connection to the first cell terminal of a first cell via first filter circuitry; a second cell connection terminal for connection, via second filter circuitry, to a first node on a connection between a second cell terminal of the first cell and a first cell terminal of a second cell, the first cell and the second cell adjacent to one another in the series arrangement; a first cell balancing terminal for connection to the first cell terminal of the first cell and bypassing the first filter circuitry; and a second cell balancing terminal for connection to a second node on the connection between the second cell terminal of the first cell and the first cell terminal of the second cell, wherein the apparatus comprises: balancing circuitry for selectively providing a cell balancing connection between the first cell balancing terminal and the second cell balancing terminal; characterized by difference determination circuitry configured to provide for the identification of the leakage current based at least on a leak detection voltage difference comprising the difference between the voltages measured between: i) the first cell connection terminal and the first cell balancing terminal; and ii) the second cell connection terminal and the second cell balancing terminal, wherein the apparatus provides for identification of leakage current based on a filtered leak detection voltage difference and based on a predetermined threshold, the filtered leak detection voltage difference comprising the leak detection voltage difference subjected to discrete-time filtering. a first cell connection terminal for connection to the first cell terminal of a first cell via first filter circuitry; a second cell connection terminal for connection, via second filter circuitry, to a first node on a connection between a second cell terminal of the first cell and a first cell terminal of a second cell, the first cell and the second cell adjacent to one another in the series arrangement; a first cell balancing terminal for connection to the first cell terminal of the first cell and bypassing the first filter circuitry; and a second cell balancing terminal for connection to a second node on the connection between the second cell terminal of the first cell and the first cell terminal of the second cell, balancing circuitry for selectively providing a cell balancing connection between the first cell balancing terminal and the second cell balancing terminal; characterized by difference determination circuitry configured to provide for the identification of the leakage current based at least on a leak detection voltage difference comprising the difference between the voltages measured between: i) the first cell connection terminal and the first cell balancing terminal; and ii) the second cell connection terminal and the second cell balancing terminal, i) the first cell connection terminal and the first cell balancing terminal; and ii) the second cell connection terminal and the second cell balancing terminal, wherein the apparatus provides for identification of leakage current based on a filtered leak detection voltage difference and based on a predetermined threshold, the filtered leak detection voltage difference comprising the leak detection voltage difference subjected to discrete-time filtering.