Why is car battery drains overnight?

A car battery's main function is to provide electric energy to start the engine before running. The starter motor needs huge electric power to crank the engine to run. When the engine is running, it starts a charging system to provide electricity to other electrical car components and charge the battery itself.

You might find that we cannot start the car in some conditions, and there are no signs of the lights on your car's dashboard. It can indicate that your car battery is draining overnight. So, what can cause the car battery draining overnight? Here, six reasons why your car battery may begin to drain :

1. Human Error

The first cause of car battery draining overnight is human error. Forget to shut off the radio, headlamp, foglamp, interior lamp, or even the car door is not tightly closed, so the illumination door lamp still lights up.

All those electric components will use your car battery's electric energy continuously so it can be draining your car battery overnight.

2. Weak battery

The next cause of car battery draining overnight is from a weak battery. A weak battery can happen if used for a long time (old battery), broken battery cell, runs out of battery water, etc. Read: Car battery leaking ? Here's what to do

The weak battery has no chance to keep all of the charging electric energy from the alternator. It means that the car battery cell has broken down partially to keep all incoming electric energy. In a short time, the battery cell will damage entirely and make the battery dead.

3. Faulty charging system

A faulty charging system can be the cause of your car battery draining overnight. The charging system in a car is built from several components such as fuse, alternator, battery, harness, connector, etc.

All those components can be broken over time which will affect the battery charging system directly.

Below are some components that will affect the charging system, especially for the possible cause of why the car battery draining overnight :

Broken fuse for the charging system.
Bad alternator.
Loose connector for the charging system.
Corroded battery terminals.
Broken alternator belt.

4. Parasitic drain

The other cause of car battery draining overnight is because some parasitic drain is happening too much on your car battery. Some parasitic drain is normal, for example, for your car security alarm systems, radio presets, etc. But, too much parasitic drain would drain your car battery overnight.

Too much parasitic drain will happen if there are many electrical problems in your car. For example, short circuits, loose connectors, defective car relays, etc., will be brought too much parasitic drain. Some of these problems would drain your car's battery energy quickly.

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5. Extreme temperature

Most car batteries use a chemical reaction to charge and discharge electrical energy. Chemical reaction processes in car batteries also depend on temperature. If the ambient air temperature is at extreme levels, this can also affect the car battery's performance.

For example, temperatures of extremely hot (over 100 degrees Fahrenheit) or cold (under 10 degrees Fahrenheit) can cause abnormal chemical reaction processes. The worst is that it can drain your car battery overnight.

6. Incorrect modification or replacement

The last cause of car battery draining overnight is incorrect modification or replacement. Suppose you use too many audio-video accessories like a power amp, huge subwoofer, big screen TV, etc., without uplifting your car charging system specification. It could drain your car battery overnight.

Another incorrect modification or replacement is using the wrong car battery type and size from your car battery specification. Different types and sizes of car batteries would negatively affect charging systems such as undercharge and battery draining overnight.