Hi mike71
The volt meter recommended in the third post above is the way to go. As you can see, it is a "loaded" volt meter. This means the volt meter puts a load on the battery, then it reads the voltage. If you check the battery frequently you will learn to note when the voltage drops, which is an indicator of a problem. Most people do not realize that some batteries can read full voltage, yet any kind of load will drive them to a worthless condition. As a point of interest, and also to teach you a lifetime piece of information, connect a voltmeter to your car battery. It should read 12 volts or slightly more. Now crank the engine to start it, and note what the voltmeter reads. The voltmeter will drop down below 12 volts, while cranking, and after the engine starts, will go to close to 14 volts. If I do this on a cold day, and the voltage drops below 9.5 volts while cranking, I replace the car battery, assuming all other conditions are or have been normal.