AO Silver Member
Join Date: Mar 2003
Location: Dublin, Ireland.
My understanding of the battery light is that it lights when insufficient power is available from the alternator and a charge has to be taken from the battery.
This can be demonstrated by running a car at normal idle when warm, then placing a high current draw on the car (turn on full beams, rear demister, wipers, windows). The car will increase the RPM to maintain a charge voltage of 13.5v to 13.8v DC. The charge current may drop significatantly when this occurs.
i.e. a car should only demand current from a battery when starting.