This invention is a portable emergency EV charging system for controlled vehicle-to-vehicle energy transfer. It allows a donor vehicle, service battery or mobile power source to charge a stranded EV safely when no charging station is available. The system uses selectable or bidirectional power electronics, vehicle communication, authorization, pre-charge control, contactor sequencing and safety monitoring. It checks insulation, leakage, voltage, current, temperature, cable lock and emergency stop status before and during transfer. It can limit delivered energy, record charging data。