Car Won't Start — Dead Battery
A dead battery is the most common reason a car won't start. Most batteries last 3–5 years before losing the ability to hold a charge. Jump-starting gets you moving again, but you need to address why the battery died.
Can I Drive?
Not yet — the car won't start. Once jump-started, drive immediately to a shop or auto parts store for a free battery test. Don't turn the engine off until you get there.
Most Likely Causes
- 1
Battery end of life
Most batteries last 3–5 years. Cold weather dramatically reduces battery capacity. If your battery is over 4 years old, it's likely time for replacement regardless of the cause.
Check the date sticker on top of the battery — format is month/year.
- 2
Parasitic drain
Something is drawing power when the car is off — a stuck relay, a dome light left on, an aftermarket accessory, or a failing module. The battery dies over hours or days.
Suspect a drain if the battery is new but keeps dying.
- 3
Failing alternator
The alternator charges the battery while driving. A failing alternator means the battery slowly drains even while driving — you'll eventually stall in traffic.
If the battery warning light comes on while driving, suspect the alternator.
How to Diagnose It
- 1
Turn the key to the start position and listen. Rapid clicking = low battery power. Slow, heavy cranking = weak battery. Complete silence = dead battery or bad connection.
- 2
Check battery terminals. Disconnect the negative cable (black), then positive (red). Look for white or blue corrosion on the terminals. Clean with a wire brush and baking soda solution.
- 3
Have the battery load-tested at any auto parts store (free). A battery at 12.6V sitting still but dropping to 9V under load is failed and needs replacement even if it jump-starts fine.
How to Fix It
Battery end of life
Battery replacement is one of the easiest DIY jobs. Disconnect negative cable first, then positive, remove the hold-down bracket, lift out the old battery, and install the new one in reverse order.
Parasitic drain
Use a multimeter in series with the negative cable. A reading over 50mA with all doors closed and accessories off indicates a drain. Pull fuses one at a time to isolate the circuit.
Parts & Tools
Enter your vehicle on the home page to get vehicle-specific parts links.
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Mistakes to Avoid
- Don't connect jumper cables in the wrong order — negative to negative, positive to positive.
- Don't replace the battery without testing the alternator — a bad alternator will kill a new battery.
- Don't buy the cheapest battery — get the correct group size and at least 600 CCA for your climate.