Short answer
If the battery light comes on while you drive, the car is not charging and runs on the battery alone. Turn off the AC, radio, seat heaters and chargers, but keep the headlights on if you need them. Drive straight to a mechanic or home without turning the engine off. If the temperature gauge climbs or the steering gets heavy, pull over and stop: the belt may have broken.
Safety first
If the temperature gauge rises, the steering suddenly gets heavy or you smell burning, pull over safely with your hazard lights on and turn the engine off. On a highway, get as far from traffic as you can.
What to do when the battery light comes on
1The battery light comes on while you drive
The car is not charging. The engine now runs on what is left in the battery, and that does not last long.
Read all the steps
- The battery light comes on while you drive. The car is not charging. The engine now runs on what is left in the battery, and that does not last long.
- Turn off everything you do not need. AC or heater fan, radio, seat heaters, phone chargers. Keep the headlights and wipers on if you need them to drive safely.
- Watch the temperature gauge. In many cars one belt turns the alternator and the water pump. If the needle climbs or the steering gets heavy, pull over and turn the engine off.
- Drive straight to a shop, do not shut it off. With a weak charge, the car may not start again. Go directly to a mechanic or home, with no stops on the way.
- Have the alternator and belt tested. A mechanic checks the alternator, the belt and the battery. Many auto parts stores test the charging system for free.
- Call a mechanic to test the charging system Especially if: the battery light stays on, or comes back after a restart.
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Why it happens
- A failing alternator, the part that charges the battery while the engine runs.
- A broken, loose or slipping serpentine belt, the belt that turns the alternator. You may hear squealing.
- A loose or corroded battery cable, or a bad battery.
- A blown fuse or a damaged wire in the charging system.
What not to do
- Do not keep driving with the temperature in the hot zone or with heavy steering.
- Do not stop for errands on the way: the car may not restart.
- Do not just replace the battery and hope. If the alternator is bad, the new battery dies too.
When to call a mechanic
- The battery light stays on, or comes back after a restart.
- You hear squealing from the engine or see a broken belt.
- The car died after the light came on and will not start.
- The lights dim or flicker while you drive.
Frequently asked questions
Can I drive with the battery light on?
Only a short way, straight to a mechanic or home. The car runs on battery power alone and will die when it runs out. Turn off everything you do not need to stretch it.
Does the battery light mean I need a new battery?
Not always. Most often it means the car is not charging, usually because of the alternator or the belt. A charging system test tells you which part failed.
How long can a car run with a bad alternator?
It depends on the battery and what is turned on, often from a few minutes to under an hour. Do not count on it: drive straight to help.
Why did my battery light come on and then go off?
It can be a loose connection, a slipping belt or an alternator starting to fail. Have the charging system tested soon, before it leaves you stranded.
What does the battery light look like?
A small rectangle with two posts on top and a plus and a minus sign inside. On most dashboards it is red.
Can a mobile mechanic replace an alternator?
Often, yes. Many mobile mechanics replace alternators, belts and batteries in your driveway, so you do not have to drive on a dying charge.