When your vehicles alternator goes out the alternator will not be able to charge the vehicles battery.
The failed alternator will also stop supplying electricity to the engine and other parts of the car.
So when your alternator fails your battery will then supply the needed electricity to your cars engine system.
When that happens your vehicles battery will start draining and losing power because it's keeping the engine running.
Eventually after about 5 or 6 miles or sometimes sooner your engine will shut off because there's not enough voltage to the fuel pump, engine coils etc.
So a failing alternator means your engine won't be able to run and you'll be stranded.
if you think your alternator is failing you can have it tested at places such as Autozone or other auto parts stores or even an automotive shop.
If the alternator has failed completely you won't be driving too long so get it replaced with a new one before the bad alternator does leave you stranded.