Your battery's terminals are the points of connection between your car battery and your battery cables, and are the points through which electricity actually flows from your battery to the various electrical systems in your car. If your battery terminals begin to degrade, which can happen naturally due to age and wear, your battery will no longer be able to provide adequate power to your vehicle. If this occurs, it can leave your vehicle unable to operate, and you stranded on the side of the road. Thankfully, there are some warning signs that you can keep an eye out for to help determine when it's time to head into a mechanic to have your battery replaced.
The easiest to spot warning sign that your battery terminals are beginning to fail is if you notice that you have trouble starting your vehicle. This can take the form of you having to turn the ignition multiple times for the engine to turn over, a rapid clicking sound when you turn the ignition, or a handful of other similar issues.
Another sign of a failing battery terminal that is fairly easy to spot is if your headlights begin to dim or flicker while you are driving. This is because the connection between the battery cable and the terminal isn't completely secure, resulting in an uneven power supply to your car's electrical system. For this reason, you may also notice reduced performance in other systems, like the windows, power steering, and the radio.
Another sign of battery terminal failure, though it can sometimes point to issues with the battery cables or the battery itself, is a burning smell. This usually points to an improper flow of power from your battery, causing some component (usually the insulation on the battery cables) to begin to burn and melt. If you notice a burning smell while driving, you should pull over right away and call a mechanic, as if left unchecked this could cause serious damage to the components of your car.
If you notice any of the above symptoms, you'll want to pop open the hood and visually inspect the terminals on your battery. Most of the time, faulty terminals are caused by a buildup of corrosion that actually eats away at the terminals. Terminals that have been rusted away will no longer be able to pass power through them, leaving your battery as good as dead. If you can see corrosion on the terminals, you'll know that it's time to have the entire battery replaced by an auto repair service.