Nearly every automotive problem is an inconvenience of some sort to the driver, but that's doubly true in the winter months. For example, a car that won't start due to a dead battery is one of the most common issues when it comes to vehicles. However, there's a big difference between trying to get a car jump started in the summer and standing out in the cold freezing in the middle of winter.
With that in mind, drivers should take care to ensure they diagnose their battery problems correctly the first time, so they won't have to guess if their car will start when they head out in the middle of a blizzard.
A common mistake that many drivers make is thinking that they have a battery issue when it's actually an alternator problem. These two devices are closely related, and both are critical to starting a vehicle. Almost everyone knows that if they turn the key and don't hear the engine at all, it's likely related to the battery, and this is true. Yet many are quick to replace their battery or solely focus on that without checking the alternator as well.
If you know how the vehicle works, an alternator issue makes sense. The alternator holds the charge that then gets passed on to the battery. When the engine is running, it turns a crankshaft, which provides mechanical energy. The alternator's job is to convert that into electric energy, which can then be used by the battery. Think of the alternator like a bridge between the engine and battery and you'll have a good idea of why exactly its so important.
If the alternator's not working, then it will give many of the same symptoms as a dead battery. However, one crucial difference is in the headlights. Turn your car's headlights on, then rev the engine. If the lights dim or get brighter, it's likely the alternator that is causing the issue, not the battery. If you think back to how the alternator works - taking the mechanical energy and converting it to electricity - then it makes sense that stepping on the accelerator can affect the lights with a faulty alternator.
Of course, this isn't 100 percent reliable - you'll likely need to use an electric multimeter if you want to confirm exactly what the issue is.