A vehicle, system, and control method include a traction battery having a plurality of cells, a temperature sensor configured to measure battery temperature of the traction battery, an electric machine powered by the traction battery and configured to provide propulsive power to the vehicle, and a controller configured to control at least one of the electric machine and the traction battery using an estimated battery power capability or estimated battery state of charge based on battery parameters initialized upon requesting activation of the traction battery with an open circuit voltage that varies based on elapsed time from the traction battery becoming inactive. The open circuit voltage may be estimated using parameters including a first resistance, a second resistance in series with the first resistance, and a capacitance in parallel with voltage across the capacitance initialized based on an exponential function of the elapsed time.