When to Change Your Car's Battery. There are several signs that indicate the battery in your car is failing and needs to be replaced. Sluggish engine cranking and unusual electrical problems like flickering headlights are telltale signs of trouble, though they may also indicate problems with your car's alternator. You should also replace your battery if it is bulging or has a rotten egg smell.
If belt tension is correct, then the next item to check is the alternator itself. You now have two choices - you can test the alternator yourself with a simple test using a voltmeter, or you can have the test performed by a professional. If you choose to do the test yourself, then you will need a DC voltmeter, or a multimeter. Such a unit can be purchased at most auto supply stores, hardware stores, department stores, home improvement stores, etc.
Locate a replacement fuse. It must be the rated for the same amperage as the original fuse that operated the window mechanism. The amp rating should be printed on the fuse, and it should also be listed in your owner’s manual. Do not use a fuse with a higher amp rating, as this may lead damaging the electrical components of your vehicle. Push the new fuse straight down into the cradle. The fuse must be "set". This means that it does not move or wobble. Turn your car key to the "on" position. This provides power to your windows and allows you to test them. You need not start your car. Test your windows. Confirm that they go up and down without restriction.
Sometimes, what people bother so much about turn out to be problems whose solutions are extremely obvious. This conversely means that checks for electrical problems in cars should start at the most obvious locations; the battery being a good example. Sometimes, a case of a car failing to 'start' or something of that sort could be simply as a result of an electrical contact breakdown at the battery. Here all that is required in the name of auto electrical repairs is something as simple as filing the terminals that connect the car to its battery.