INTERNAL HEATING OF A BATTERY

A battery heating method and a battery heating system for a vehicle battery. The battery heating system includes a vehicle battery, an auxiliary energy storage device, a direct current to direct current converter and a processing circuitry. The processing circuitry is configured to cause the battery heating system to operate in a first mode wherein the direct current to direct current converter is configured to control a current to flow through the vehicle battery in a first direction and operate in a second mode wherein the direct current to direct current converter is configured to control a current to flow through the vehicle battery in a second direction.