It is important to be able to diagnose overcharging in a car battery. An overcharging car battery will eventually cause damage to the battery and even other electrical components of your car. You should be particularly concerned if your car battery is charging more than 15 volts. This can the result of a few issues which makes it important to diagnose overcharging in a car battery.
Start your car. You may need to use jumper cables to get it started. When you get the engine going, remove the cables and measure the voltage that runs through the battery terminals. The voltage should be somewhere between 12.8V and 14.7V. Anything higher than 14.7V indicates overcharging in the battery.
Check for a faulty regulator if you find that the voltage regulator works like an electrical current that runs volts through the battery. If the voltage regulator goes bad, it can overcharge your car battery.
Measure the voltage from the alternator. Again, the voltage should show a measurement between 12.8V and 14.7V. When you diagnose an overcharging battery, you need to always take a close look at the alternator because the alternator may be sending too much voltage to the battery.
If you notice higher voltage over a tenth or more, try cleaning the battery terminals first by removing the terminals and using a brush or other cleaning item. Reinstall the terminals and spray with terminal lubricant. You can visit an auto parts store to see if they will perform a diagnostic test to check the alternator, but before doing that, make sure you know how old your battery is first.