How long does a car battery charger take to fully charge a battery?
Unless it’s a “quick charge”charger then over-night is typical to get a decent charge. If the battery light was not on when the car was running then it’s not the alternator. If there’s any white crud growing on the battery terminals this can insulate the battery connections and it may not recharge while driving the car or if you hook up a charger to it. Most batteries will last the length of the warranty period plus a few months if driven around town with some highway miles and they will last way past the warranty period if you do mostly highway miles and keep the terminals clean (service like every other year or once a year if parked outside all of the time). Most places that sell batteries will do a free charging system diagnostic and this checks the battery, alternator, and starter. Good Luck!