8 Things That Can Drain Your Car Battery
You try to start your car in the morning, but nothing happens. You probably hear a clicking sound, but that’s about it. The car hasn’t been parked that long. It was starting just fine the previous night, and there’s no way the battery could have gone flat that fast- you convince yourself. Well, there is! And it happens to the best of us.
Several things can drain your car battery, from bad alternators to parasitic draws and adverse weather conditions. In this article, we’ll discuss these factors and how to diagnose/troubleshoot what is draining the battery.
What is draining my car battery?
Here are 8 things that can drain your car battery:
Alternator issues
The function of the alternator is to recharge the car battery and supply power to the car’s electronic components when the engine is running. Thus, when the alternator is faulty, it won’t recharge the battery, and these electronic components will draw power from the battery, causing it to drain when you’re driving.
Note: A bad alternator can also overcharge the battery, which causes the battery fluid levels to drop.
The alternator can also drain the battery, which is the exact opposite of what it should be doing- recharging the battery. This happens when the alternator diode is faulty or the alternator fuse is blown. A faulty diode can draw charge from the battery back through the alternator to the ground.
Old battery
Old car batteries typically die quicker than newer car batteries. They also drain faster than healthy batteries when the weather gets too hot or too cold. The typical lifespan of car batteries is 3-5 years. If you notice that your battery dies quicker after the 3-year mark, maybe it’s time to get a new one.
Short drives
You can also drain your car battery by taking way too many short drives. When starting the engine, the starter motor draws a large amount of voltage from the battery, causing a massive loss of charge. The alternator recharges the battery, but only works when the car is running. Thus, you should keep the car running long enough for the alternator to fully recharge the battery. Shorter drives result in insufficient battery recharge, and the battery gradually drains and dies.
Extreme temperatures
When the weather is extremely hot or cold (above 100 degrees Fahrenheit or below 10 degrees Fahrenheit), lead sulfate crystals build up on the battery plates. Consequently, the battery needs more time to recharge and is likely to die if you take shorter drives that won’t keep the alternator on long enough to recharge the battery.
Parasitic draws
The car’s alarm system, clock, radio presets, and in some cars, the computer module continue to draw a small amount of power from the battery even when the car is off. However, if any other component apart from these is also sucking the juice from the battery when the car is off, this is referred to as parasitic draw and can cause the battery to die. Parasitic drain can be due to factors like leaving the trunk/doors open, leaving the glove compartment lights on, leaving the headlights on, or faulty relay switches.
Corroded or loose connections
If the terminal connections on your battery are loose or corroded, it affects the entire charging system. Consequently, the car’s radio, lights, and other electronic and electrical components may continue to draw power from the battery even when the car is running. Make sure the connections are secure and clean the terminals to remove corrosion.
To properly clean corrosion, dust, and debris off your battery terminals. Mix baking soda with water. Then, dip an old toothbrush or a wire brush in the solution and use it to brush the terminals clean.
Leaving the keys too close to the car
If you store your key fob too close to the car after parking the vehicle, the keyless entry system continues to communicate with the car and can cause the battery to drain. To ensure the key fob doesn’t drain your car battery, keep it at least five feet away from the car.
Note: Key fob drains shouldn’t be cause for concern if your car battery is new and healthy. Older batteries that are already weak are, however, likely to suffer significant drain if the fob is kept too close.
Self-discharge
Car batteries naturally self-discharge, even when in storage. However, the standard self-discharge rate is 0.1V per month and shouldn’t be cause for concern. Extremely high temperatures above 130 degrees Fahrenheit significantly increase the self-discharge rate. As such, the battery drains faster and may die if the car stays parked for several days or weeks.
Note: Other factors that can increase the battery self-discharge rate include the battery type and battery technology. For instance, batteries with AGM (Absorbent Glass Mat) technology have a slower self-discharge rate compared to flooded batteries.
Signs of a drained car battery
The car won’t start/is slow to start
You can tell that your car battery is flat if the car is slow to start or won’t start at all. A large voltage is required to start the car. A fully-charged battery is usually at 12.7V or higher. When the battery is drained, the voltage drops to 11.8 or lower. Thus, it’s unable to provide enough power to start the car.
The battery warning light is on
When the battery is low, the battery warning light will come on. However, the illuminated warning light can be due to other problems too, and doesn’t always mean that the battery is drained.
Sulfate buildup on the battery terminals
Check the car’s engine bay to see whether there are sulfate deposits on the battery terminals. The buildup is usually grainy or salt-like. You may also notice corrosion buildup on the terminals.
Note: Apart from the above signs, other warning signs of a dying car battery include dimming dashboard lights, the car making unusual noises, and car accessories like the radio and air conditioning system not functioning.
What is the difference between a drained and a bad battery?
A drained battery is one that’s completely discharged but can be jump-started or recharged to 12.7V or higher. On the other hand, a dead battery is one that has lost the ability to hold a charge and cannot start the car even if you attempt to recharge it.
How do I troubleshoot what is draining my car battery (find out)?
You can use a digital multimeter to determine whether the level of parasitic drain from your car battery is excessive and which components are the culprits. Follow the steps below:
- With the car battery fully charged, connect one of the multimeter leads to the negative battery terminal and the other to the negative cable. Set the multimeter to the ‘current’ setting and note the reading on the multimeter’s display.
- If the parasitic draw exceeds 85 milliamps, head to the fuse box to determine which electronic component is sucking more juice from the battery than it should. Leave the multimeter connected to the battery and pull out the fuses one by one, noting the reading. When the reading drops significantly, you’ve found the parasitic component.
- Once you’ve found the component, take the necessary measures to stop the excessive parasitic draw. It could be as simple as replacing faulty relay switches, turning off a dome light, or repairing a glove box that’s not closing properly.
FAQs
What can drain a car battery instantly?
A car battery can drain instantly when bad weather combines with other factors. For instance, if the battery is already old, there’s a defect within the charging system, and the weather gets extremely cold outside, your battery could instantly drain to below 50% DOD. Freezing conditions can drain battery power by up to 60%.
Why does my car battery keep dying while parked?
Your car battery keeps dying while parked since it’s old and cannot sustain the car’s alarm, radio memory, and clock for too long. To prevent the battery from going flat when the car is off, connect a 12V trickle charger, which will recharge the battery at the same rate it’s discharging.
What is a battery parasitic drain?
Parasitic battery drain is when current continues to be drawn from the car battery even after you’ve turned off the engine. A parasitic drain is considered normal if the draw is below 85 milliamps, as components like the alarm system and internal clock need to stay powered even when the vehicle is off. However, excessive parasitic battery drain is a problem and can be due to a bad alternator diode or a bad battery.
Does parasitic drain affect my battery lifespan?
Yes. Excessive parasitic drain causes consistent charge deprivation, reducing the battery’s lifespan. Regular deep discharge beyond 50% DOD (Depth of Discharge) causes stress on the battery plates, resulting in shedding and poor conductivity. In the long run, the battery cannot take charge, thus prematurely reaching the end of its service life.
References
I. The Universal Technical Institute (UTI): What is Parasitic Battery Drain?
