Battery / Charging System Light

What it means

Shown as a small battery with plus and minus marks, usually red, this light means the charging system is not supplying enough power; the cause is usually the alternator, its belt or wiring rather than the battery alone. It is normal for it to glow at key-on before the engine starts and then go out; if it comes on while driving, the car is running on battery power only and may stop before long.

Related lights: Master Warning LightPower Steering Warning LightCheck Engine LightEngine Temperature Warning Light

Symptoms5

• Red light on while driving.
• Dim headlights or dashboard lighting.
• Other warning lights appear, or electrical items such as the air conditioning or radio stop working.
• Squealing from the engine belt or a smell of burning rubber.
• Hard starting, or the engine stalls after driving for a while.

Possible causes6

• Failed alternator or its internal voltage regulator.
• Broken, loose or worn engine belt, or a failed tensioner.
• Loose or corroded battery terminals, or a poor ground cable.
• Blown main fuse in the charging circuit or a damaged alternator cable.
• Internally failed battery that will not hold a charge.
• Charge management software fault on some newer cars (less common).

How to diagnose5

1. Switch off non-essential loads such as the air conditioning and radio, and head to the nearest workshop without switching off the engine if possible.
2. Once stopped, look to see whether the engine belt is present and intact, and check the battery terminals.
3. Measure battery voltage with the engine running; it should be clearly higher than with the engine off. Compare with the manufacturer specification.
4. At the workshop: load-test the alternator and test the battery with a battery tester.
5. Check fuses, the cables between alternator and battery, the ground points, and any stored codes.

How to fix6

1. Clean and tighten the battery terminals and repair the ground cable.
2. Replace the blown fuse or damaged cable in the charging circuit.
3. Replace the engine belt or tensioner if broken or loose.
4. Replace the battery if it fails a load test.
5. Repair or replace the alternator if confirmed faulty.
6. Start the engine after the repair and confirm the light goes out and charging voltage is within specification.

The cost starts with cleaning terminals or replacing a fuse or belt, and reaches the upper end when the alternator and battery are both replaced.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions