Dead car battery: jump it safely and find out why

Before you jump-start: safety first

AAA also advises removing metal jewelry such as rings and watches, wearing safety glasses and gloves, confirming both cars use 12-volt systems, and keeping cables well away from belts and fans.

How to jump-start a car safely

You need jumper cables and a working car (or a charged jump pack). This is AAA‘s order for a jump-start:

1. Park the cars close, but not touching, and turn both off.
2. Red clamp to the dead battery’s positive (+) terminal.
3. Other red clamp to the good battery’s positive (+) terminal.
4. Black clamp to the good battery’s negative (-) terminal.
5. Last black clamp to clean, unpainted metal on the dead car, such as a thick bolt on the engine block, not the dead battery.
6. Start the working car and let it run 3-5 minutes, then try the dead car.
7. If it starts, leave both running connected another 3-5 minutes, then remove the clamps in reverse order.
8. Drive 20-30 minutes without stopping so the battery can recharge.

If the car won’t start after a jump, or starts and stalls within 10-15 minutes, AAA says the alternator is the likely problem rather than the battery. See car won’t start for other causes.

Why car batteries die

• Age. AAA says most batteries last three to five years. Batteries in cooler northern climates can last five years or longer; in hot southern climates, about three. AAA puts AGM batteries at five to seven years.
• Heat. AAA notes under-hood temperatures can top 200 degrees Fahrenheit in hot weather, which wears batteries faster.
• Cold. NHTSA says battery power drops with the temperature, which is why a weak battery may give out in cold weather.
• Things left on. Lights, the radio, chargers and screens all draw from the battery when the engine is off.
• Parasitic drain. A fault that keeps drawing power after the car is off, such as a module that won’t sleep or a stuck light. A battery that keeps dying overnight points here.
• Short trips and sitting. AAA says short drives don’t let the battery fully recharge and suggests limiting trips under 10 miles; a car that sits can go flat in a month or two.
• Corrosion. White or bluish crust on the terminals disrupts the flow of power, per AAA.

Symptom, likely causes, and what a mechanic would check

A mechanic who can test the car will know more than any guide.

Recharge or replace?

A battery that died once because the lights were left on often recovers with a jump and a long drive, or a charger. AAA points to replacement when the battery won’t hold a charge, is more than three to five years old, or tests below about 25 percent (around 11.8 volts at 80 degrees Fahrenheit); a healthy battery reads about 12.6 volts with the engine off. AAA suggests annual testing once a battery reaches three years old.

If the car sits for long stretches, a battery maintainer (a smart charger that stops when full) can keep it topped up. Check the cold cranking amps rating on a replacement matches your owner’s manual, especially in cold climates.

Can a mobile mechanic fix it on the spot?

Yes. Battery testing and replacement is one of the most common mobile jobs, usually done in the driveway or parking lot; see mobile battery replacement. The mechanic can also test the alternator and starter while there. Tracking down a parasitic drain can take longer, but it is often doable on site.

Prices vary by vehicle and city, and the mechanic quotes after testing. Some sellers add a core charge that is refunded when the old battery is returned. See mobile mechanic cost.

What to do next

If a jump works, drive to recharge and get the battery tested soon. If it keeps dying, or you would rather not jump it yourself, find a mobile mechanic in your city or send a request. Mention the battery’s age if you know it and whether it has died before.

If you are not sure a mobile visit fits your situation, read roadside assistance vs a mobile mechanic first. A mechanic who can see the car will know more than any guide.