# Battery warning light on: alternator or battery? _Updated: 8 November 2026_ **Short answer:** The battery warning light means the battery is not charging while the engine runs, and the cause can be the alternator, the belt, a poor connection or the battery itself. Do not drive further than you must, because the car can stop suddenly. > **The service we recommend: Alternator repair** An alternator that doesn't charge: check, rebuild or new alternator. We tell you the price when you tell us the model. [More about the service](https://autoindustrija.rs/en/services/alternator-repair) ## 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 charging:** The 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 rubber:** The alternator may be faulty. After that the engine can cut out suddenly. - **Belt worn or snapped:** A 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 cable:** The 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 fuse:** No current passes through a blown fuse, so charging does not work. - **Battery at the end of its life:** After charging or a jump start, it soon goes flat again. [More about battery replacement](https://autoindustrija.rs/en/services/car-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](https://autoindustrija.rs/en/advice/car-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](https://autoindustrija.rs/en/services/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. ## Frequently asked questions ### The battery light is on, but the battery is new. How? The light does not show how old the battery is, it shows whether it is charging. When even a new battery keeps going flat, the fault is most likely in the alternator. That is why we check the alternator, the belt and the cables between them. ### The battery light comes on and goes off. What does it mean? The charging fault comes and goes. The cause can be the connection on a battery terminal or a cable that has worked loose from vibration, but also the alternator. When the lights and dashboard lights also flicker, that is a sign of a faulty alternator. Take the car for a check as soon as possible, because when the alternator fails completely, the car soon stops. ### Can I jump-start the car if the light is on? Yes, the cables help you get going. But if the alternator is not charging, the battery will go flat again while you drive. If the engine dies as soon as the cables are removed, the alternator is not charging. [More about what to do when the car won't start](https://autoindustrija.rs/en/advice/car-wont-start) Have a question about your car? Message us on WhatsApp or call 067 774 1606. ## Read also - [Car dashboard warning lights: meaning and when to stop](https://autoindustrija.rs/en/advice/dashboard-warning-lights) - [Check engine light (engine warning light): what it means and what to do](https://autoindustrija.rs/en/advice/check-engine-light) - [Car won't start: what to check first](https://autoindustrija.rs/en/advice/car-wont-start) --- Page on the website: https://autoindustrija.rs/en/advice/battery-warning-light auto-industrija, Belgrade. Phone and WhatsApp: +381677741606. E-mail: kontakt@autoindustrija.rs.