This information can save you cost and trouble if your battery goes dead, and almost all motorists have this problem at one time or another.
Batteries can fail suddenly, so if one day you notice your car turns over sluggishly when you try to start it, have the battery checked as soon as you can, or check it yourself. You may save yourself an embarrasing and long wait for a jump or a tow truck.
There are really only two reasons batteries fail. Either the battery itself has gone bad, or there is something wrong elsewhere in the electrical system. To find out if it is simply a bad battery, and therefore save yourself the cost of professional diagnosis, do this: Take the caps off the battery. Most ‘sealed’ batteries actually have removable caps. If the liquid level in one cell is much lower than the others, chances are the battery is bad. If the liquid level is low in all cells, you may need to simply raise the levels with distilled water, and then the battery will work fine again.
If the liquid levels seem alright, you can take the center wire off the distributor so the car won’t start. Have someone hold the key in the start position for 15 seconds while you look into the top of the battery (wearing safety goggles). If you see bubbles forming in only one cell of the battery, that cell is bad and the battery must be replaced. If no bubbles form, or all cells form equal amounts of bubbles, the problem is elsewhere. Check for corrosion on the battery connections.
Please remember that battery acid can be injurious to your health, especially your eyes, and can damage clothing.