Tip #19: If the car dies while driving, suspect the alternator before the battery
A weak battery usually shows itself when you try to start the car. A failing alternator usually shows itself while you are driving, with dimming lights, a battery warning light and, eventually, a car that stalls. A jump will not fix an alternator.
Tip #19 in one line
A weak battery usually shows itself when you try to start the car. A failing alternator usually shows itself while you are driving, with dimming lights, a battery warning light and, eventually, a car that stalls. A jump will not fix an alternator.
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Call nowWhat each part does
The battery supplies the burst of power that starts the engine. Once the engine is running, the alternator generates electricity to run the car and recharge the battery. When either fails, the car ends up with no power, which is why the two get confused.
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Call nowSigns pointing to the battery
A slow crank or a clicking sound when you turn the key. The car starts fine after a jump and runs normally all day, then will not start again the next morning. The battery is old, has corroded terminals or looks swollen.
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Call nowSigns pointing to the alternator
The battery or charging warning light comes on while you are driving. Headlights and dashboard lights dim or flicker, especially at idle, and brighten when you rev the engine. Power windows slow down, the radio cuts out, or warning lights appear one after another.
A slipping or broken drive belt can cause the same symptoms, because the belt is what turns the alternator. A squeal on start-up or a belt that looks glazed or cracked is worth showing to your mechanic. On some cars the same belt drives the power steering and water pump as well, so a broken belt can also mean heavy steering and overheating.
A whining or grinding noise from the front of the engine, or a smell of hot electrical parts, can also point to the alternator or its belt.
The car starts after a jump but dies again after a short drive. That is the classic sign: the car ran on what was left in the battery, and nothing was recharging it.
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Call nowWhat to do
If the charging light comes on while you drive, turn off every load you can, such as the heater fan, rear defroster, heated seats and radio, and head for a safe stop or your mechanic, not a long highway run. Expect the car to stall when the battery runs out.
A jump start technician tests both the battery and the charging system, so you learn which one failed before you spend money. If the alternator is the problem, the car needs a mechanic, and a local tow is quoted on the same call to (908) 444-0129. More on breakdowns is on the blog.
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Call nowMore on batteries
Keep reading, or go back to every post on the blog.
- Dead car battery in a New Jersey winter: why it happens and what to do
- Tip #11: Jump-start in the right order, and finish on bare metal, not the battery
- Tip #12: Never jump a battery that is swollen, cracked, leaking or frozen
- Tip #18: Test an aging battery in the fall and replace it on your schedule, not the weather's
- Tip #20: A battery that dies every few days usually has something draining it
- Tip #85: Test your battery every fall once it is a few years old
- Tip #87: If your battery keeps dying, have the alternator load-tested at a shop
- Tip #93: Modern cars and EVs drain their 12-volt battery while parked
- All posts
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