A method performed in a vehicle control unit for controlling an electric machine (EM) of a heavy-duty vehicle, wherein the heavy-duty vehicle comprises an energy storage system (ESS) connected to the EM, the method comprising obtaining an energy absorption capability of the ESS, determining an amount of regenerated energy by the EM during braking, and configuring an efficiency level of the EM in dependence of the energy absorption capability of the ESS relative to the amount of regenerated energy by the EM during braking.