A jumped battery only has the charge the alternator has put back. The RAC suggests driving normally for around 30 minutes after a jump, then recharging fully with a proper charger. If the battery is old or faulty, it may go flat again the next time you park, however long you drive.
Right after the jump
The AA's procedure is to leave both cars running for around 10 minutes before disconnecting the leads, then restart your car. After that:
- Keep the engine running. Don't switch off for a quick errand.
- If you can, drive normally for around 30 minutes, avoiding heavy traffic (RAC).
- Keep heated screens, seats and the blower to what you need for safety.
Why it might not last
- Not fully recharged. The RAC says a full recharge is best done with a quality charger over several hours.
- Worn battery. It may start the car today and fail tomorrow.
- Charging fault. If the car cuts out while driving, or the battery light is on, see dead battery or alternator?
Next steps
Recharge at home (how long to charge a car battery), then have it tested. If it fails the test, replace it.
Frequently asked questions
Can I switch off straight after a jump?
It's better not to. The battery is still low and the car may not restart.
Is idling as good as driving?
No. Driving normally for around 30 minutes is the RAC's suggestion.
What if it goes flat again the next day?
The battery or charging system likely needs testing or replacing.