Richard, if the battery is old & shot with dead cells, would the alternator refuse to charge and hence you get a flickering charge light ? even if the alternator is healthy
As Doug suggests the warning light sits between alternator field circuit and battery which in turn is permanently connected to alternator output. Once the two are at similar voltage little or no current flows through warning light so it extinguishes.
Generally alternators do require a kickstart in the first place unless there is residual magnetism in the field rotor. This is supplied to the rotor to create a magnetic field via the current (0.25 amp) flowing through the illuminated (3 watt) warning light bulb when ignition first turned on. The battery is therefore required to provide this but would be in a very poor state not to do so. Once the alternator comes online, sometimes with help of a few revs above idle, it becomes self sustaining via a trio of dedicated diodes bleeding back from the output to maintain the field, with the output voltage controlled by the field regulator.
Once working with some load, it technically doesn't need the battery therefore, although if it presented by same with an open circuit and load dropped, volts would surge, regulator wouldn't be able to cope and something would blow, probably diodes - Phew!
