The light tells you charging is not working
If the light is on while the engine runs, the alternator is not charging the battery or there is a fault in the charging. The car then runs only on power from the battery.
When you turn the key, the battery light comes on, and as soon as the engine starts, it must go off. This is how the car shows that the light works.
If the light does not come on even when you turn the key, that is also a fault that needs checking.
The alternator, belt, a connection or the battery is to blame
Alternator not chargingThe alternator, a part the engine turns with a belt, charges the battery. When it doesn't, the lights dim or flicker, and the windows, air conditioning and radio work badly. The car starts hard or the battery keeps going flat.
Loud grinding from the engine while driving, then a smell of burning rubberThe alternator may be faulty. After that the engine can cut out suddenly.
Belt worn or snappedA worn belt squeals when you start the car. When it snaps, the steering can get heavy and the engine can overheat.
Poor connection or damaged cableThe connection on a battery terminal, plus or minus, or a cable works loose from vibration. The light is on although the alternator and belt are fine.
Blown fuseNo current passes through a blown fuse, so charging does not work.
Battery at the end of its lifeAfter charging or a jump start, it soon goes flat again. More about battery replacement
A weak battery, a loose connection and a worn belt give the same signs, so everything involved in charging is checked.
Can you drive with the battery light on?
Do not drive further than you must. The car uses power from the battery, and when it is flat, the car can stop suddenly.
How far you can drive depends on
- How strong the battery is.
- What is switched on: lights, air conditioning, heaters.
If the steering gets heavy or the temperature needle climbs along with the light, the belt may have snapped. On many cars the same belt drives the water pump, so the engine can overheat. Stop as soon as it is safe and switch off the engine.
If along with the light you hear the belt squealing, the alternator may not be charging at full power. In that case too, take the car for a check as soon as possible.
What to do until you get to the check
- Switch off what uses power and you can drive without. The radio, air conditioning, rear window heater and seat heaters drain a battery that is no longer charging.
A check shows whether the battery or the alternator is to blame
A check shows whether the battery or the alternator is to blame, before you buy a new part. Don't buy a new battery before the alternator is checked: if it isn't charging, it will drain the new one too. More about why a battery keeps going flat
An alternator can often be repaired, it does not have to be new
An alternator can often be repaired, and when a repair doesn't help, a rebuilt or new one is fitted. More about the auto electrician
The belt is replaced on your car's service schedule. It is replaced earlier when it cracks, frays, turns shiny or squeals. Oil leaking onto the belt damages it faster.
