Why can you drive all night with headlights on, but if you turn the car off and then turn them on, your battery dies by morning?
In: Technology
When your engine is warm it heats up the headlight fluid which reduces the amount of power they consume. When your car won’t start in the morning irs usually because the headlight fluid is low and needs to be filled up.
While the car is running, some of the energy it produces is put through an alternator, which in turn charges the battery while the battery is being used for the headlights. If the car is using the battery without running or burning gas for fuel, the battery will drain because no energy can run through the alternator to charge the battery again
When the car is driving the engine charges the battery. When the car is off the battery drains and can no longer kick the engine on. The battery is used to do the car equivalent of pulling a rip cord on a lawn mower.
While the car is on the alternator is on, which generates electricity to charge the battery, and power the electrical systems. When the car is off, it’s running on pure battery.
In addition to the engine not charging the battery while off as others mentioned, the battery itself just isn’t made for that. Lead-acid batteries are great for providing high amperage for extended periods i.e. running the engine starter. You can crank the engine over for a fair amount of time and the battery is going to supply it with enough juice to work until the bitter end.
If you graph the power output of a battery, other batteries will look like a downwards slope, meaning as they use their capacity up the power they’re supplying at any given time goes down. Lead-acid would look like a plateau with a steep drop off at the end. But the end comes quicker overall. Which is why we need alternators.
Your engine contains a part called an alternator – this is a small generator that makes electricity as the engine runs.
So when you are driving normally, the battery is needed to start the engine, but after that point the alternator is producing enough electricity to keep running the engine and also power the lights, radio, ac, etc and the battery does nothing.
When you turn off the engine, the battery now had to power everything, use too much power and the battery ribs flat and will no longer have enough power left to start the engine again.
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