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hatsune_aru t1_j5nxahk wrote

Reply to comment by dbx999 in What is the difference between a battery and a capacitor? by Buford12

The actual regulation in a car is done by the ECU or some circuit inside the alternator that limits the output voltage to a certain amount.

The battery is mostly there so that when there is a load transient, the regulator mentioned above can have a relaxed response time--the battery takes up the slack when there's a sudden load increase or decrease.

If a control system has to react quickly, it's more liable to instability like oscillation and divergence. Better to keep it safe by making it slow to react, especially if you already have a big ass battery that can smooth things out that you need to start the car.

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PromptCritical725 t1_j5qtyxu wrote

This is a reason people with bigass car stereos add capacitors. Large sudden power draws like amps driving large bass hits can cause equally large drops in system voltage. The capacitor act to "stiffen" the system by providing reserve of current that can be drawn and replenished much more rapidly than a battery can. This keeps the voltage more consistent.

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