This system is called a "take over" system that when the switch is on ( the bicycle is being ridden or generator is on the wheel spinning), the generator's/alternator's higher voltage ( 6.3volts) will switch the lights from battery power (4.5volts) to generator power using a relay which in terms charging the battery at the same time. When the bicycle comes to a complete stop, the current reduce voltage allowing the relay to "spring" back to battery power which allows the lights to remain on. The accessories of coerce are remain on battery power unless they take more amperage then the battery can put out.
