One tiny correction- - - -the purpose of a charging system is to provide power to everything- - - -ignition, lights, heater blower, sound system, etc. and then use whatever capacity is left over to recharge the battery. Most alternators are sized to carry the current demand of all the accessories, plus around a 25% over capacity for battery charging. Adding heavy current demand stuff without increasing the charging system capacity proportionally can lead to a chronically under charged battery from making up the added load.
Jerry
