The car battery is one of the most critical parts of a vehicle, and it's one that even amateur mechanics may find themselves dealing with from time to time. A dead battery is a very common problem, and jumping one is usually not something that a driver should call a tow truck or mechanic for. Thus, even drivers who never open up the hood of their vehicle may have some experience with their car's battery.
Unfortunately, this has also lead to a lot of misinformation about car batteries. A driver may hear a story from a friend or perhaps has experience on their own with a car battery and misinterpreted what actually happened. Thus, many myths have popped up centered around this part of the vehicle.
First it helps to understand how the battery works. Essentially, this part is connected to the electrical system in your vehicle, and is also responsible for triggering the spark that starts the engine. So how does a battery provide power over years and years? Some drivers might think that the battery is simply very large and will eventually drain like any other normal battery. While a car battery is a great deal larger than the batteries found in your cell phone or laptop, the reason it can provide energy over a long period of time is due to the alternator.
The alternator is essentially the bridge between mechanical and electric energy in the car. The crankshaft turns as the engine runs, which provides power to the alternator. The alternator converts that to electricity, which recharges the battery. Many people overlook the important role of the alternator, but this is exactly why a car battery can drain overnight. If you leave your headlines on, the battery is being used, but since the engine is turned off, the alternator never gets any power to replenish it. That leads to a dead battery. A battery can also die if the alternator stops working - unfortunately, many people are quick to blame things on the battery and get that replaced instead, only to find their new battery dies almost immediately.
The alternator also plays a role in another common myth, which is that your battery will recharge once you drive it around for a bit. The idea behind this theory is true, but it's highly variable. It could take hours to recharge a dead battery, and idling the engine or stop-and-go trips are unlikely to do so. Alternator power could also be diverted to things like heated seats or other electrical systems, which slows down the recharging time. This is why many drivers wake up to a dead battery the day after they give themselves a jump - it never fully recharged in the first place.
Some people know about the alternator, but don't know how to diagnose an issue. Back in the 1970s, the recommended way to do so was to disconnect the battery from the engine while it was running. This is not safe to do today - in fact, it could destroy the electrical components of the vehicle completely. Instead, try the "headlight test," which involves pushing the accelerator down when the car is in park. If the lights dim or get brighter, you'll probably need to replace your alternator.
Finally, the role of temperature comes into play often when talking about battery. One old myth is that storing batteries on a cold concrete floor will discharge them. This is true of very old batteries, but modern versions seal in their charge much better, and it's safe to store them just about everywhere. Some drivers think cold weather is bad for batteries as well. While the engine is a bit more difficult to start in the winter, hot temperatures actually cause batteries to lose their charging capacity at a much faster rate - car batteries in warmer climates tend to only hold their charge two-thirds as long as colder climate batteries.