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6 Things That Can Drain Your Car Battery

Batteries Plus Blog - Power - by Bryan Veldboom - updated on 8/6/2021

Woman on her phone holding a child looking under the hood

A dead car battery can be a real headache. Finding yourself stranded isn't just inconvenient, if you find yourself in bad weather, it can be dangerous too. Fortunately, with a little TLC, you can help keep your battery from dying unexpectedly. Here are six of the most common causes of a drained battery and what you can do to help prevent it from happening.

Parasitic Draws

A parasitic draw is anything that uses energy from the vehicle in your car or truck. Some parasitic drain is perfectly normal in order to power things like interior lighting, clocks, radio settings and alarm systems. The problem occurs when your electrical system isn't functioning properly. Issues such as faulty wiring, bad fuses or interior lights that fail to shut off will continue to drain your battery while it's idle.

What You Can Do About It

How do you stop a car battery from draining when not in use? You can avoid parasitic drain on your battery by unplugging optional equipment such as cell phones and chargers when you park your vehicle for the night. You can also turn off every light in your vehicle and make sure that your trunk, glove box and doors are all fully closed and latched before leaving your vehicle.

Driving habits

The way you drive has a significant impact on your battery. Your battery expends an enormous amount of energy starting your engine, which is then recharged by your alternator while you drive. If you take a bunch of short trips in a row, however, the alternator doesn't have enough time to recharge your battery, which will continue to be drained each time you restart your vehicle.

What You Can Do About It

Be sure to vary your driving by taking longer, uninterrupted trips in between shorter stops. While the amount of time needed will vary from vehicle to vehicle, driving your car for about fifteen minutes should be sufficient to replenish the energy used to start the engine.

Loose or Corroded Battery Terminals

Loose or corroded battery terminals can impair your battery's ability to transmit power, preventing your vehicle from starting. You may also experience slow cranking or notice a rapid clicking sound when attempting to start the engine.

What You Can Do About It

Clean or tighten your terminals by following the steps below.

Step 1: Remove the cover from the battery box, if one is present, and store it in a safe place.

Wipe loose dirt and moisture from the battery using an old rag. Move loose wires out of the way to gain access to the battery terminals.

Step 2: Determine whether the vehicle has a positive or negative grounding system.

Most modern vehicles are negatively grounded -- the black (negative) wire goes from the battery to the vehicle chassis. Older vehicles may have a positive ground. If you are uncertain, consult the vehicle manufacturer's manual.

Step 3: Disconnect the battery cable that goes to ground.

Use an adjustable wrench, a screwdriver or simply unscrew the plastic knob depending on the system used on your vehicle. Place the disconnected cable where it cannot accidentally fall back onto the battery terminal. For example, if the vehicle has a negative ground, disconnect the negative cable. When the grounding cable has been disconnected, and only when it has been disconnected, should you undo the other cable. Place the end somewhere safe where it cannot fall back on to the battery.

Step 4: Fit a battery terminal cleaner over one of the terminals and rotate it to remove corrosion, debris and oxidized metal.

Continue rotating until the terminal is shining. Alternatively, you can use a combination of a wire brush and emery paper to clean the terminal until it shines. Repeat the process on the other terminal.

Step 5: Clean each of the battery cable clamps, one at a time.

Scrub each terminal clamp thoroughly using a wire brush and emery paper until it is clean and shiny. Wipe it clean with an old rag and smear petroleum jelly all over the metal surfaces.

Step 6: Wipe any debris from the top of the battery, then reconnect whichever cable was disconnected last.

So, for a negative ground vehicle, reconnect the positive cable first. Ensure that the terminal clamp sits as far down on the terminal as possible, then tighten it. Tighten it until you cannot move the clamp by hand. Do not over tighten it as you could damage the battery terminal.

Step 7: Reconnect the remaining cable, again pushing the clamp fully down on the battery terminal and tightening it until you cannot move it by hand.

Extreme Weather

Both high heat and extreme cold can have a negative impact on your auto battery.

Heat issues:

  • Evaporation: Under the hood, a car battery can reach internal temperatures of 140 degrees or higher. This causes the fluid inside it to evaporate, damaging your battery's internal structure.
  • Overcharging: High heat can cause the voltage regulator or other charging system components to malfunction, overcharging the system and killing your battery.
  • Corrosion: Extreme temperatures cause your battery's internal lead plates to corrode, leading to deterioration.

Cold issues:

  • Reduced Capacity: At 32 degrees, your battery's capacity drops by 20 percent. At -22 degrees, it can drop by 50 percent.
  • Thicker Engine Oil: Cold temperatures cause engine oil to thicken, forcing your battery to work harder to turn over the engine.
  • Reduced Recharge Rate: Remember how we mentioned that your alternator recharges your battery? Well, in lower temperatures, your battery recharges slower, meaning you have to drive further to charge it back up.
  • Load Increases: We tend to use more applications during the winter to help offset the cold and keep the windshield clear. Running things like the heater, windshield wipers, defroster and seat heaters increases the load on your battery, causing it to recharge even slower.

What You Can Do About It

In summer, park in the shade as often as possible to help keep your vehicle's temperature down. In winter, park your car indoors if you have the option. Since both heat and cold can drain your battery, you may want to use a charger when your vehicle's not in use, or carry a portable jump starter in your vehicle in case your battery dies. If you live in an area prone to extreme temperatures, you may want to invest in an AGM battery that is designed to perform in a broader range of temperatures.

Bad alternator

Since your alternator is responsible for recharging your battery, it stands to reason that if your battery isn't performing properly, the alternator may be at fault. What are the signs of a bad alternator?

  • Dim or overly bright lights
  • A consistently dead battery
  • Slow or malfunctioning accessories
  • Trouble starting or frequent engine stalling
  • Growling or whining noises when starting the vehicle
  • Smell of burning rubber or wires
  • Battery warning light on the dashboard lights up

What You Can Do About It

Have your alternator tested as soon as possible to see if it's the problem. Obviously, if your alternator is down it's going to be hard driving your vehicle to a mechanic. For some vehicles though, it is possible to jump start the engine with a bad alternator. If you can generate enough electricity to run essentials such as the onboard computer, fuel pump and fuel injectors, you should be able to drive it to the nearest repair shop.

Your Battery is Too Old

If none of the issues already mentioned are at fault, it's possible you have a bad battery on your hands. A vehicle battery typically lasts between three and five years. If your battery is older than that, it may be time to replace it.

What You Can Do About It

Bring it to your nearest Batteries Plus location and have it tested for free. Our experts can tell you if you need a replacement and help you choose the best option if you do. You can also shop our selection of car and truck batteries online and take advantage of our free battery installation (available on most vehicles at most of our locations).

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