It’s more likely than you think!!
The next time you turn on your car, leave the key in the “RUN” position without turning it all the way to start and look at the lights that will appear on the dashboard. You should notice somewhere a small battery icon.
And there, folks, is the fail, for despite being a glowing battery icon, this light does not indicate a problem with the vehicle’s BATTERY.
I’m not going to put up schematics and stuff because that’s just getting too technical* for this. In short, the battery light indicates a problem with your vehicle’s ALTERNATOR.
The ALTERNATOR light, which inexplicably has a freaking BATTERY painted on it, indicates that the vehicle’s alternator is not charging the battery when it SHOULD BE. It came on when you turned the ignition on without starting the engine because the alternator is not being spun by the engine. Once the engine is running it should go out, because the alternator is being spun and is generating electric current to recharge the battery.
You may see the light occasionally flicker under any situation that keeps the alternator from spinning. Driving through a puddle may wet the belt and cause it to slip, causing the light to flicker. Forcing the engine RPM too low on a vehicle with a manual transmission will also make it flicker. In either case it will go out once the alternator spins back up to operating speed.
If the alternator fails to generate power, due to a broken/failed belt (you may also notice a loss of power steering assist and air conditioning!), the light will come on. The car will stop running once the battery runs out of power.
If the alternator itself fails, it may also turn on the battery light. Note that the battery light signal is generated by the alternator, so a particularly rotten failure of the alternator’s internal electronics may not necessarily turn on the light. My father had the electronic voltage regulation controls inside the alternator on a Volvo 740 fail like this while driving on the Florida’s Turnpike in the middle of nowhere – the first sign of trouble was when the antilock brake controller (dimly) illuminated its fault light due to the low input voltage!
Soooo… why not label the light “ALTERNATOR”? Even the execrably designed NABI 40LFW transit bus has the light labelled as “GEN STOP”. Suggesting that it means the GENerator has STOPped working is infinitely more useful.
* me, resisting the urge to geek out about how this actually works? INSANE