How to jump-start a car without frying anything

A dead battery is the most common reason a car won't start, and jumping it takes about ten minutes if you do it in the right order. The order matters: the last connection is the one that sparks, and a battery can vent flammable hydrogen gas.

Before you connect anything

• Check your owner's manual. Some newer cars — especially hybrids and EVs — have a dedicated jump-start terminal under the hood instead of using the battery directly, and a few say not to jump them at all
• Both cars off, parking brakes on, keys out, not touching each other
• Look at the dead battery. If it's cracked, leaking, bulging, or frozen solid, don't jump it — call for a tow or roadside service
• Find the terminals. Positive is marked + and usually has a red cover. Negative is −

The connection order

1. Red clamp → dead battery's positive (+)
2. Other red clamp → good battery's positive (+)
3. Black clamp → good battery's negative (−)
4. Last black clamp → bare, unpainted metal on the dead car's engine block or frame, away from the battery — a big bolt or bracket works

That fourth one is where people go wrong. Clamping onto the dead battery's negative terminal works electrically, but it puts the spark from the final connection right next to the battery, where hydrogen gas can collect. Grounding to the engine block moves that spark away.

Starting it

1. Start the good car and let it run for 2–3 minutes
2. Try starting the dead car. If it doesn't catch, wait another few minutes and try again — don't crank for more than about 10 seconds at a time
3. Once it starts, remove the clamps in reverse order: black from the engine block, black from the good battery, red from the good battery, red from the formerly dead battery. Don't let the clamps touch each other while any are still connected
4. Drive for at least 20–30 minutes (not idling in a parking lot) so the alternator can put some charge back in

If it keeps dying

A battery that needed one jump after you left the lights on is probably fine. One that dies again within days is telling you something:

• Batteries typically last about 3–5 years — heat shortens that. Auto parts stores will test your battery and charging system for free
• If a new-ish battery keeps dying, the alternator may not be charging it, or something is draining it while the car is off
• Corroded terminals (white or green crust) can cause the same symptoms — cleaning them is a cheap first step

The no-second-car option

A portable lithium jump starter (roughly $50–100) lets you do this alone, with no second car. Same idea: clamps on, follow its instructions, start the car. It's one of the more useful things to keep in a trunk.

Quick reference

• Red to dead (+), red to good (+), black to good (−), black to bare metal on the dead car
• Start the good car first, wait a few minutes, then try the dead one
• Remove clamps in reverse order
• Drive 20–30 minutes afterward to recharge
• Keeps dying? Get the battery and alternator tested free at a parts store