A vehicle includes a battery configured to operate at a current, during a drive cycle, in a nominal current range for a time greater than in a maximum current range. A controller is programmed to output a voltage based on the current according to a gain calibrated to be greater in the nominal current range than in the maximum current range to increase resolution in the nominal current range. The gain may be based on an exponential function or piecewise linear function of the current. The gain may increase as a magnitude of the current increases. A second controller receives the voltage and derives a battery current according to an inverse of the gain.