The best time to conduct this test is about 12 hours after turning off the car. When you first wake up in the morning, after not driving all night. The first step is to get a battery and a voltmeter. A voltmeter measures electric potential difference from two separate points in an electric circuit. A voltmeter will let you know if. There are a few reasons that can cause your battery to have a high voltage. Your battery could have a loose connection. Loose connections disrupt. The high voltage causes all kinds of problems with your vehicles. Cars are operating on a more electrical basis now with more vehicles being hybridor electric altogether. When your. Yes, you can drain the access voltage from your battery. The easiest way is to turn on your high beams and just allow them to stay on. Using.