If you have ever turned the key on your car only to hear a clicking sound, then you know the frustration of a dead battery. And the frustration can be compounded if you have the battery charged, but the car won't start again the next day. The battery may be experiencing a current drain, or current leak, while the vehicle is not being used. It is not usually apparent where to start looking for the leak, but there is a method for finding the problem.
Turn off the car, open the bonnet and disconnect the negative battery cable from the battery.
Place the 12-volt test light into the car battery circuit. Do this by connecting one end of the test light to the negative terminal of the battery and the other end of the test light to the end of the negative battery cable.
Look at the bulb on the test light and the brightness of its glow. There should be a faint glow because of a couple of systems that always draw current, such as the car's clock or computer chip. If you are experiencing significant drain, however, there will be a bright glow from the test light bulb.
Start removing fuses one at a time from the fuse panel in the car. Check the test light each time you remove one of the fuses. If the light remains on while you have a fuse removed, that system to which the fuse belongs is not the cause of the problem. Put that fuse back in place and move on to the next one.
Identify the system that is causing the problem by noting when the test light bulb goes out when a fuse is removed.