Function curve describing the maximum battery charging rate (in kW) at a given charge level (in kWh). Map keys represent charge levels that are non-negative floating point values in units of (kWh). Map values represent charging rate values that are positive floating point values in units of (kW). Given charge levels must cover the entire range of [0, BatterySpecifications.targetChargeInKilowattHours], otherwise the BatterySpecifications instance is considered invalid. The charging curve is considered piecewise constant instead of being interpolated. Defaults to an empty container. Note: For a user-planned ChargingStop, this parameter is also required. If one or more values are not set, the route calculation will fail as an invalid parameter error.