Car batteries are designed to last a pretty long time, but eventually they will wear out and need to be replaced. The general rule of thumb is that a battery should last about four years before it begins to run out of juice. However, if you notice telltale signs of a dying battery before the expected expiration period, you might need to replace it.

The most obvious sign a battery needs to be replaced is if the car will not start without being jumped. This can also point to problems with the alternator or the starter, and you should test the battery before replacing it. If you replace a battery you believe to be dead, when the actual problem lies with the alternator, this could potentially drain the new battery as well. If there is a deeper issue, it will need to be addressed before replacing the battery.

Car batteries can be weakened by a number of factors. Extreme temperatures can negatively impact the part's performance. When the weather is below freezing, a battery only generates about 60 percent of its charge, according to AAA. Hot weather can also affect the battery's performance and charge capacity. Driving habits play a role in the function of a car battery as well. Taking frequent short trips or not driving a vehicle for long periods of time can drain the battery.

If you suspect the battery is dead, an electronic tester is the most accurate way to be sure. You can also visually inspect it for signs of leaks and corrosive buildup around the terminals. If the terminals are corroded, you should clean them off and give the battery another try. This may have been restricting the battery's ability to function properly.

Be sure to wear gloves when inspecting the battery, as it is filled with an electrolyte solution that consists partly of sulfuric acid. The mixture can damage the skin, so it is best to exercise caution when working with a car battery. Sulfuric acid also has a very pungent scent similar to that of rotten eggs. If you detect this odor, you may be dealing with a leaky battery.

Once you've determined the current battery needs to be replaced, you will need to remove it and install a new battery. Stay tuned for tips on car battery replacement.