Battery Equivalents and Replacements

Can You Jump Start a Car With a Bad Alternator?

When the car starting battery is discharged, one can jump-start a car with another car's battery using jump-start cables or using a car jump starter.

However, there are many reasons why the battery is dead in the first place, including parasite load over a longer period of time, bad or simply old battery, or a bad or faulty alternator.

If the battery is almost new and there are no loads that would discharge the battery, and one nonetheless has to jump-start the car, there is a great probability that there is something wrong with the alternator or charge regulator, leading to the question, if the car can be jump-started with a bad alternator...

Published: November 10, 2021.

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The answer is simple - Yes, You can jump-start a car with a bad alternator.

But, can You drive such a car, that is another question.

Bad or Faulty Alternator or Charge Controller

When the car's alternator or its charge controller goes bad, the car's battery is not being charged or it is being insufficiently charged.

Modern cars depend on electric power heavily, not just for powering alarms, GPS, maps, multimedia devices, etc. but also for powering the car's central computer, fuel pump, and a few more critical components which doesn't require much power, at least not as some multimedia devices, but nonetheless, they do require a reliable source of electric power.

What happens when the engine is running and the car battery voltage starts to drop?

Well, first the car will warn the user about a voltage drop, but the engine will continue to run - in most cases, this message will be in the form of a warning or stop message.

But, after some time, either the fuel pump will stop causing the engine to stop or the central computer will stop causing the engine to stop too, or the computer will shut down the engine to prevent any damage and signal "General Electric/Electronic Failure" or will give some similar error message.

Of course, a large "Stop" on the dashboard will signal the user to stop the car before all of this happens, but, if You wondered what would happen if You decide to ignore the dashboard's "Stop" sign, now You know. :)

However, if the alternator is providing at least some power to the car, it is possible to jump-start a car and drive it directly to the car's repair shop - just be sure to turn off everything that is not essentially needed.

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How to Jump-Start a Car Using Jumper Cables?

In order to jump-start a car using jumper cables, one needs another car with a good battery and working alternator.

So, park the second car (one with a good battery) next to the first car (one with a discharged battery) and:

- connect a red clamp to the positive (+) terminal (usually the red one) of the dead battery,

- connect the other red clamp to the positive (+) terminal (the red one) of the good battery,

- connect a black clamp to the negative (-) terminal (usually the black one) of the good battery,

- connect the other black clamp to the negative (-) terminal (the black one) of the bad battery,

and let the second car run for a few minutes - this will provide some "surface charge" to the bad battery and help both batteries crank the engine.

Note: while being connected, the alternator of the second car is under a larger than normal load, so don't keep the cars connected for a very long time.

After the first car cranks its engine, disconnect the cables in reverse (start with the negative clamp from the bad battery).

If the first attempt was not successful (the electric system of the first car didn't have enough charge/power for the car's starter to kick in), let both cars stay connected for a few more minutes - just be sure to monitor the dashboard of the second car, just in case - and try again to crank the first car's engine.

If it starts, good - turn off everything non-essential and drive to the car repair shop.

If it doesn't start - call the tow service.

Disconnect the cables in reverse starting with the negative clamp from the dead/bad battery.

How to Jump-Start a Car Using Car Jump Starter?

Car jump starters are small and compact devices that feature lithium rechargeable batteries and control electronics that enable them to provide insanely strong currents, considering their weight and size - and they are relatively cheap as well.

A good car jump starter can fit most glove compartments, backpacks and can be carried around - just be sure not to leave them in the car during freezing cold days or hot summer days.

noco boost gb40

If the car's engine doesn't want to start, connect the jump starter to the battery (starting with the positive clamp!), turn ON the jump starter, let it analyze the battery, and when the jump starter signals, crank the engine - it is that simple.

Note: lithium jump starters are very easy to use, but their exact starting procedures may differ a little bit, so keep the Owner's Guide with your car jump starter, just in case.

Disconnect the jump starter and if You suspect that the bad alternator and/or charge controller are the reason for heaving dead battery, drive directly to the car's repair shop - just be sure to turn off every non-essential electric load.

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Long Story Short: As one can see, there are several ways of cranking the engine of the car with the discharged/bad battery.

However, the question is if that car is safe for driving - after cranking the engine, check the dashboard and if there are no errors or warnings, drive to the repair shop.

Also, if You are using car jumper cables, having two cars connected for a longer period of time can overload the alternator and/or charge controller of the car with a good battery - again, keep your eyes on its dashboard.

Whatever You do in such a situation, stay safe - after all, it is your own responsibility.

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