How Long Does It Take for the Alternator to Charge the Battery?
For a battery that’s in perfect condition but has been drawn down for some reason, it will take a bit of time to rejuvenate its capacities. That can be from several engine starts with only short drives in between or using accessories without the engine on, for example. How quickly the alternator takes to charge the battery tends to vary widely based on a few factors.
- If the battery isn’t 100% healthy, it can take longer to charge.
- If your car’s accessories, heater fan, radio, or other power-consuming systems are running, there’s less power available to charge the battery.
- A battery recharges slower when it’s near full capacity compared to drawn down.
- The alternator’s amperage dictates its maximum charging rate.
As an example, an 80-amp alternator might be recharging a battery with a capacity of 75 amp-hours (stated as Ah) from 80%. However, the alternator requires some power for the car’s other electrical functions, so only 50 amps are available for charging the battery. Theoretically, it would take 90 minutes to fill the battery from empty. Topping up 20% would require one-fifth of that time, or about 17 minutes.
Again, that assumes all parts and systems are operating at full capacity and doesn’t consider the slower charging rate for the near-capacity battery. The good news? Your car will start easily if it’s at 80% charge, and the alternator will have no trouble maintaining it at that level if it’s operating properly.