a flexible substrate able to conform to a surface of a battery cell to be monitored;

a plurality of first-level prediction units integrated onto the flexible substrate, where each first-level prediction unit is positioned at a different location on the flexible substrate to each other first-level prediction unit, and each first-level prediction unit comprises at least one sensor to generate sensor signals indicative of a physical state of the battery cell and first-level prediction circuitry to generate a predicted battery cell status value in dependence on the sensor signals received from the at least one sensor of that first-level prediction unit;

second-level prediction circuitry arranged to determine a prediction result in dependence on the predicted battery cell status values generated by the first-level prediction circuitry of each first-level prediction unit; and

a communications device to output the prediction result at least when the prediction result indicates an occurrence of a critical event;

wherein the second-level prediction circuitry is arranged, responsive to being triggered to determine the prediction result:

to determine, for each first-level prediction unit, a current predicted battery cell status based on one or more predicted battery cell status values generated by the first-level prediction circuitry of that first-level prediction unit; and

to determine the prediction result in dependence on the current predicted battery cell status associated with at least one first-level prediction unit;

wherein the current predicted battery cell status is selected from a set of possible statuses that comprise at least a normal status and one or more critical event statuses, the normal status indicating normal operation of the battery cell, and each critical event status indicating an abnormal behaviour of the battery cell;

wherein in response to a determination that the current predicted battery cell status determined for at least one first-level prediction unit differs from the current predicted battery cell status determined for at least one other first-level prediction unit, the second-level prediction circuitry is arranged to perform a check operation before determining the prediction result; and

wherein the check operation implements a procedure to check whether the first-level prediction circuitry of each first-level prediction unit is operating correctly.