5.2.Rechargeable electrical energy storage system (REESS)5.2.1.For a vehicle with a REESS, the requirement of either paragraph 5.2.1.1.or paragraph 5.2.1.2.shall be satisfied.5.2.1.1.For a REESS which has been type approved in accordance with Part I1 of this Regulation, it shall be installed in accordance with the instructions provided by the manufacturer of the REESS, and in conformity with the description provided in Part 2 of Annex 6 to this regulation.5.2.1.2.The REESS shall comply with the respective requirements of Paragraph 6. Of this regulation.5.2.2.Accumulation of gasPlaces for containing open type traction batteries that may produce hydrogen gas shall be provided with a ventilation fan or a ventilation duct to prevent the accumulation of hydrogen gas.5.3.Functional safetyAt least a momentary indication shall be given to the driver when the vehicle is in "active driving possible mode".However, this provision does not apply under conditions where an internal combustion engine provides directly or indirectly the vehicle's propulsion power.When leaving the vehicle, the driver shall be informed by a signal (e.g. optical or audible signal) if the vehicle is still in the active driving possible mode.If the on-board REESS can be externally charged by the user, vehicle movement by its own propulsion system shall be impossible as long as the connector of the external electric power supply is physically connected to the vehicle inlet.This requirement shall be demonstrated by using the connector specified by the car manufacturer.The state of the drive direction control unit shall be identified to the driver.5.4.Determination of hydrogen emissions5.4.1.This test shall be carried out on all vehicles equipped with open type traction batteries. If the REESS has been approved under Part Il of this Regulation and installed in accordance with paragraph 5.2.1.1.this test can be omitted for the approval of the vehicle.