What is the purpose of the 'High-Voltage Safety Disconnect' (Hochvolt-Trennschalter / Rettungstrennpunkt) on electric and hybrid passenger buses?

1. To turn off the passenger reading lights
2. To allow emergency rescue services and mechanics to completely de-energize the high-voltage traction battery circuit (600–800 V) in the event of an accident or rescue cutting operation
3. To speed up the charging of mobile phones
4. To change the bus destination display text