can a car battery be jumped if it's completely dead

[WyattLee]

Yes, you can usually jump-start a car with a completely dead battery, but success depends on why it's dead. If the battery is simply drained from leaving lights on, a jump start is typically effective. However, if the battery has failed due to old age, internal damage, or has been completely dead for weeks, a jump may not work or the car may not stay running.

A standard 12-volt car battery is considered completely discharged when its voltage drops below roughly 10.5 volts. While jumper cables or a jump pack can provide the necessary power to crank the engine, the battery itself may be too degraded to accept a charge. A key sign of a permanently damaged battery is sulfation, where lead sulfate crystals harden on the plates, preventing chemical reactions.

The process is similar to jump-starting any battery, but it might take longer. After connecting the cables correctly (positive to positive, negative to a ground on the dead car's engine block), let the booster car run for 5-10 minutes before attempting to start the dead vehicle. This allows some charge to transfer. Once started, you must drive the car for at least 20-30 minutes to allow the alternator to recharge the battery. If the battery cannot hold a charge after this, it needs replacement.

Battery Voltage (Engine Off)	State of Charge	Likelihood of Successful Jump-Start
12.6V - 12.8V	100%	Not Needed
12.0V - 12.4V	50-75%	High
11.5V - 12.0V	0-25% (Very Low)	Moderate
Below 10.5V	0% (Fully Discharged)	Low / Conditional
Below 3.0V	Deeply Discharged / Damaged	Very Unlikely

[OLogan]

From my experience, if you just left a dome light on overnight, a jump will almost always get you going. But if the battery is more than four or five years old and gives you no signs of life—no dash lights, no click—it's probably shot. You can try jumping it, but don't be surprised if you need a tow truck and a new battery. The real test is if it dies again right after you get it started.

[Katie]

It's a bit of a gamble. The jump starter packs you can buy are great for this. If the battery is totally dead, you might need to let the pack charge it for a solid ten minutes before you even try to start the car. Sometimes it works like a charm. Other times, the battery is just too far gone and won't take a charge anymore. It's always worth a shot before calling for help.

[LiamDella]

Sure, you can try. Hook up the cables properly—positive to positive, and the negative to an unpainted metal part on the dead car's engine. Let the good car run for a while. If the dead battery is just drained, it should start. But if it's an old battery that's failed, you might get a start, but it'll die the second you turn off the engine. Then it's time for a new one.

[KylieLynn]

Technically, yes, but it's not a guarantee. A completely dead battery might have internal damage that prevents it from holding a charge, even if the jump-start gets the engine running. The critical factor is the battery's health before it died. A new battery that was accidentally drained is a good candidate for a jump. An old battery that has been slowly failing is not. After a successful jump, a long drive is essential to recharge it.