If car batteries are so big then how come then drain so quick when you leave the radio or lights on overnight?

1.63K views
0

If car batteries are so big then how come then drain so quick when you leave the radio or lights on overnight?

In: Technology

They’re not designed to provide low power for a long time, they’re designed to provide a lot of power fast. Under normal operation they’ll discharge once really powerfully to crank the engine when you start the car, then recharge and wait for the next time.

You can run headlights and radios and whatever else off the battery briefly, but automotive batteries are extremely inefficient in this setup.

They’re big, but they only hold a limited amount of charge, like all batteries. Car batteries are designed to deliver super high amps when the engine is started, in a single burst, in order to literally turn a huge chunk of metal that’s subject to internal resistance within the engine. They can only do this when they have sufficient internal voltage.

If you leave the lights or radio on, they will drain capacity from the battery, until eventually there won’t be enough voltage left to deliver that super high power burst you need when the car starts. There will likely be enough residual voltage to run other stuff, but as soon as you try to start the car, it’ll drain that all off.

Size =/= battery capacity
What makes a battery last longer is more amp hours and less amps being drawn by your vehicle. It takes awhile to drain a battery fully with just lights. Usually it just doesn’t have enough juice to start the vehicle.