A battery cell monitoring system comprises a flexible substrate able to conform to a surface of a battery cell to be monitored, and 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. 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 is 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 is used to output the prediction result at least when the prediction result indicates an occurrence of a critical event.