NOVELTY - The apparatus (118) has a memory for storing input state data representing initial parameters for estimating parameters of a rechargeable cell. A processor supports an estimator unit (212) to receive the input state data during use. The estimator unit performs extended kalman filtering in respect of a state transition model and an observation model using the input state data to generate output state data. The processor evaluates a criterion associated with part of the output state data and generates a control signal in response to evaluation of the criterion during use.    USE - Cell monitoring apparatus for use in a battery monitoring apparatus of an integrated circuit for use in a powertrain for a vehicle (all claimed) e.g. electrically powered vehicle and hybrid electric vehicle such as plug-in hybrid vehicle.    ADVANTAGE - The apparatus improves current sensor precision, so that SoC estimation performance can be improved. The apparatus adopts offset compensation techniques so as to improve estimation of the SoC of a battery in an accurate manner. The apparatus can couple an isolator between adjacent measurement units so as to improve safety performance in a reliable manner.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a battery monitoring apparatus    (2) a powertrain for a vehicle    (3) a method for monitoring a rechargeable cell    (4) a computer program product comprising a set of instructions for monitoring a rechargeable cell    (5) a tangible, non-transitory readable medium comprising a set of instructions for monitoring a rechargeable cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a battery pack controller of an automotive vehicle including a cell monitoring apparatus.    Cell monitoring apparatus (118)    Primary current sensor (152)    Secondary current sensor (156)    Transceiver (200)    Estimator unit (212)    Current sensor processing unit (218)    Non-volatile memory unit (220)