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
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.
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