Not reliably. The alternator keeps a healthy battery topped up while you drive. It isn't designed to fully recover a deeply flat battery. After a jump start, the RAC suggests driving for around 30 minutes, but says a full recharge is best done with a quality battery charger over several hours.
What the alternator is for
Once the engine is running, the alternator powers the car's electrics and replaces the charge used for starting. The RAC notes that jump packs and leads simply allow your engine to start, and the alternator then begins to maintain or recharge your battery.
Why a completely flat battery needs more
- The RAC says a battery that has been run flat needs to be recharged fully to be fully serviceable, and that this is best done with a quality battery charger over several hours.
- Short trips and heavy use of electrics (heater, lights, heated screens) leave little spare charge.
- A battery that has been flat for a long time may not take a full charge at all. It may need conditioning or replacing.
What to do after a jump
- If you can, drive normally for around 30 minutes, not in heavy traffic (RAC).
- Avoid switching off again soon after a jump.
- Recharge with a mains charger at home. See how to charge a car battery.
- Have the battery tested. If it won't hold charge, replacement is the fix.
Frequently asked questions
How long should I drive after a jump?
The RAC suggests driving normally for around 30 minutes, avoiding heavy traffic if possible.
Will idling recharge the battery?
The RAC's advice is to drive normally for around 30 minutes, then recharge fully with a charger.
Can a deeply flat battery be ruined?
A battery left flat for a long time may not take a full charge again. Get it tested.