Can a car battery be too dead to jump start?

(Last Updated On: May 18, 2023)

Jump-starting a car battery will work 90% of the time. If you struggle to jump-start your car, naturally, you’ll need the answer: Can a car battery be too dead to jump-start? A car battery can never be too dead to jump start. 

However, some instances will explain why you cannot jump-start a dead battery. The obvious answer being the problem isn’t battery related, the other being the capacity of the car battery or jump pack you are using, which is covered in more detail below.

Why won’t my car jump start?

To start with, the most obvious and the one that catches people is if you have a vehicle with a large battery like a Range Rover, it will have a 100 amp+ battery. Now, if you try to jump-start a Range Rover from another smaller vehicle like a Ford Fiesta with only a 55-amp battery, you will need more than a 55-amp battery. A fiesta-sized battery only has enough cranking power to turn over that sized engine.

You can still get it to work by revving the engine to 1500 rpm and keeping it connected so more amps produced by the alternator (electrical units) are transferred to the dead battery. For the same reason, this also applies to the size of the jump pack, although most are several times more amps than a typical car battery.

The other reasons the car won’t start are typically because it is not the battery at fault, and the fault lies elsewhere:

  • Faulty start cables – Most battery jump starter cables have an insulation coating, so it is difficult to see what’s happening inside the cable; if they are split, you wouldn’t be able to tell. The other thing to bear in mind is the size of the starter cables determines the size of the current they can carry and, thus, the size of the battery they can start.
  •  Faulty starter motor The starter motor internals could have failed. The starter cannot turn the crank over with a jammed starter motor, usually evident as a clicking sound when turning the key. You can sometimes tap the starter motor with a hammer to free them off, and the car will then start, with or without jump cables attached.
  •  Fuelling issue Without fuel, an engine will not run; the issue can be traced to an inoperable fuel pump, blocked fuel line, or injector problems.
  •  Bad battery terminals – Corroded or broken battery terminals need to make a better connection for the charge to be moved from the battery to the starter motor. For an electrical current to move between components, they rely on a good connection starting with the battery terminals.
  •  No engine spark – No engine spark can usually be traced back to a faulty coil pack or related components; without a spark, there is nothing to ignite the fuel.
  • Alarm issue – With a faulty alarm or immobilizer no amount of jump starting will get the car going.

How long should it take to jump-start a car?

Jump starting a car should only take about 5 minutes; however, if the battery is completely dead, you can leave the car connected via starter cables to a running vehicle. This means the running car’s alternator will generate some electrical charge passed over to the dead battery.

In icy weather conditions, you may need to leave the jump cables connected for up to 30 minutes to aid jump starting the dead battery. The only downside to this is that it will ruin the running car battery if it is weak.

What should I do if I can’t jump-start my car?

If your car doesn’t jump start from a battery pack or another vehicle, you should try ‘bump’ starting the car, but only if it is a manual transmission. 

Bump starting involves another person pushing the car along as fast as possible. When you build enough speed, rapidly releasing the clutch with the car in 1st gear will bump the start of the engine into life. This works quite well if you have a dead battery that won’t start because it relies on mechanical power turning the crank to start the car and not electrical.

You cannot bump start an automatic transmission car. If jump-starting does not work, you will need to phone a vehicle recovery company to tow the vehicle to a mechanic for inspection. You could have a faulty neutral safety switch; if you do, the car will not jump-start.

can a car battery be too dead to jump start


Can you jump-start a car in the rain?

Yes, there is no problem with jump-starting the car in the rain.

Is it safe to jump-start a car battery?

The only times jump starting a car is unsafe is if you jump start a hybrid-engine or electric vehicle. A hybrid-engine/electric car has more than one battery; they use incredibly high voltages, so it’s best left to roadside recovery to sort. The other thing is being careful not to touch the positive and negative ends of the jump cables together while they are connected to a battery. Other than that jump starting a car is perfectly safe.

Can a car battery freeze?

Yes, batteries can freeze; distilled water is inside a battery. Although it won’t happen if the battery is in good condition, a fully charged battery will freeze at -70 degrees Fahrenheit. Only a weak battery with no charge will freeze at around -10 degrees Fahrenheit. You can’t tell from the outside of a battery that it’s frozen, but a battery should thaw out before jump-starting.

Why do you ground the negative when jumping a car?

You connect the negative cable to the ground/earth to eliminate the chance of any sparks being produced, which can ignite the hydrogen gases released from a dead battery.

Do you attach red or black first when jumping in a car?

You attach the cables in the order of red first, which is the positive cable to the + battery terminal, and then the black last, which is the negative cable to the chassis or ground. You remove the cables in the reverse order, so black (negative) off first and then red (positive) last.

Final thoughts

A car battery will never be so dead it will not jump start. If you have trouble trying to jump-start your car, leave the car connected via starter cables to another running vehicle for up to 30 minutes. Then try starting the car again. If that fails, you may find that the issue is not a dead battery or a different fault altogether.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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