Symptom guide
Battery light on? It's usually the charging system
Despite the picture, the battery light usually means the charging system has stopped doing its job. The car is now running on whatever is left in the battery, and that won't last long.
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Narrow it down
What it usually means
The light is on, and everything else seems normal
The alternator, its belt or the wiring has stopped charging. Switch off the A/C, the radio and the heated seats, and head somewhere safe to park while there's still charge.
The light, plus dimming lights or a weak radio
The battery is running down. You have minutes, not hours. Find a safe place to stop.
The light, plus a squeal or a burning smell
The belt may be slipping or damaged. On many engines that belt drives other parts too, so keep an eye on the temperature gauge and stop if it climbs.
The light stays on after a jump start
If the car died, got a jump and the light is still on, it isn't charging. A new battery on its own won't fix that.
The light flickers over bumps
A loose or corroded connection at the battery or the alternator. Cheap to fix once it's found.
Mercedes: "Auxiliary battery malfunction"
A different message about a different battery. Many newer Mercedes models carry a small backup battery as well as the main one. More on Mercedes-Benz.
A guide, not a diagnosis. Two cars with the same symptom can have different faults, which is what testing is for.
Worth knowing
Before you spend money
- Many GM models vary charging output on purpose, so a single reading on a cheap meter can mislead. We test properly.
- A battery that's been run flat by a failing alternator is often damaged too, so we test both.
- Don't keep jump-starting a car with a charging fault. It runs flat again, and repeated deep drains are hard on the battery.
- If the temperature gauge rises as well, pull over and switch off.
Questions
Asked about this one
Does the battery light mean I need a new battery?
Usually not. It normally means the car isn't charging, which points to the alternator, the belt or the wiring. We test the battery and the charging system before replacing anything.
How far can I drive with the battery light on?
Not far. The car is running on the battery alone. Switch off what you don't need and head somewhere safe to park.
How much is an alternator replacement?
From $155 labor, confirmed for your car before we start. Parts are quoted first.
Other symptoms
More guides
Car won't start
Click, slow crank or nothing at all? What each one usually means, and what to check first.
Check engine light
Steady or flashing? What the light means, what to do right now, and why a free code read isn't the end of it.
Brakes squealing or grinding
Squeal, grind or shudder. What the noise usually means, and how soon to book.
Still not sure what it is?
That's what the diagnostic is for. $125, and it goes toward your repair if we do the work.
Or call or text (813) 710-5060 · 9am–9pm · 7 days