Does Draining A Car Battery Damage It?

Inserting the key in the ignition or pushing the button to ‘on’ to start the car is something you do subconsciously because you have done it so many times. Have you ever wondered how that simple action makes the car start? Better still, have you ever wondered why the very same action which always works to get the car started, sometimes just doesn’t work?

The Science behind Your Car Battery

The primary function of the battery is to provide power to start the car. Once it is running, power is provided by the alternator. The standard car battery has 12 volts. Each battery contains 6 cells, each carrying 2.1 volts. It is considered fully charged at 12.6 volts or more.

Each cell is made up of two plates, one made of lead and the other made of lead oxide. The two are suspended in a bath of 35% sulfuric acid and 65% water. The solution acts as an electrolyte. Itcauses the chemical reaction which produces electrons.

the science behind a car battery

Battery Discharge

Discharging in this context refers to utilization of the battery’s power. Battery discharge happens every time it starts the engine, runs the car radio or illuminates the headlights. When this happens, the plates in the cells slowly get coated with lead sulfate.

This is perfectly normal because it is completely reversible. If you sit in the car and listen to the radio for a couple of minutes as your passenger runs out to run an errand, the plates undergo a little sulfation. When your passenger returns and you turn on the engine to drive away, the battery is recharged and sulfation is reversed.

If you happen to leave the headlights or radio on overnight the battery gets drained because the lights and radio are drawing power from the battery when it is not getting recharged. Some drain is permissible but if it drains or discharges too far, it gets damaged.

Why Discharging a Battery Too Far Is Damaging

How far is too far? As discharge continues (without recharge) voltage drops. If it drops below 10.5 volts, it is considered fully discharged, at which point the battery will suffer irreversible damage. How so? Normal sulfation as described earlier is reversible as soon as the car is started again.

In the case of a discharged battery, the soft lead sulfate crystalizes. Once crystals are formed, the sulfation cannot be reversed.  The crystals remain in the plate and this permanently reduces the battery’s available output.

Can A Completely Dead Battery Be Recharged?

discharging a car battery

Many drivers wonder whether it is best to replace or recharge a battery after it has been drained. The purpose of the alternator is to keep the battery recharged. It was not designed to pick up a completely drained battery. If the battery is completely dead consider jumpstarting it.

How to Jump Start A Dead Battery

Do I need a new battery if it dies? Probably not. It can be jump started to bring it back to life. Before starting the process, make sure that all the cables attached to the battery are secure and free of corrosion. If there is any corrosion, clean it with a stiff brush.

Park the car with a functional battery as close to the one with a faulty one, but ensuring that the two do not touch. You could choose to have the cars next to each other facing the same direction, or nose-to-nose.

Make sure the engines of both cars are off.

Connect the first positive end to the positive terminal on the dead battery. After that connect the other positive end to the positive terminal of the charged battery. Positive jumper cables are red.

Connect one of the ends of the negative cable to the functional battery’s negative terminal. Negative cables are generally black. On the car with the dead battery, attach the remaining end of the negative cable to a grounded metal surface. You can use chassis, frame or any other suitable component as a grounding surface.

Once all the connections are properly done, start the engine of the car with a charged battery. Current will flow into the dead one and begin to charge it.

Let the engine of the car with a charged battery run for five minutes. This will allow the dead battery to accumulate charge of its own.

Try to start the other car’s engine. If it has gathered enough charge it will start without a problem. If it doesn’t start, give it more time and then try again.

Once the car which had the dead battery starts, you can now disconnect the cables. Remove them in reverse order of the way you connected them. Start by removing the grounding cable, then the negative cables and then the positive ones.

Let the car which had the dead battery run for another five minutes. This allows the alternator to recharge the battery. Now go out for a drive. Drive around for at least 20 minutes to let the battery charge fully. Drive continuously because stopping may leave you in need of another jumpstart.

jumpstarting tips

Some Jumpstarting Tips

There are some precautions to take if you decide to go the jumpstarting way. Never attempt to jumpstart a cracked or leaking battery. If your battery has either of these, replace it.

Do not allow any of the jumper cable clamps to touch. Ideally the process should be done by two people, each holding one end of the cables. The two shouldhold one clip in each hand.

Never attempt to jumpstart a frozen battery.Make sure that the battery you are jumpstarting is not dry. Inspect individual cells to confirm that they contain fluid. Add water if necessary. Use your owner’s manual for details on how to go about this.


Ideally, your car battery should never get drained but mechanical problems and human error make this a fairly common occurrence. Does draining a car battery damage it? Yes, a fully discharged battery may be recharged but it never really functions at its best again.

Jumpstarting helps to juice up dead batteries but requires extreme caution. If you have to jumpstart you battery, check the owner’s manual for guidance and have someone assist you to ensure the cable clamps never come into contact.

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