Amp meters offer a number of amazing benefits. Here are some benefits that you may find useful: 1. It's best not to overcharge your car battery because, if you don't know how many amps are flowing into your batte. When working with vehicle batteries, safety must be the number one priority. Despite their. How should a battery charger read when it is charged to the full? On a 12 amp charge, the needle will be around 6 amps to indicate that the battery has been fully charged. When y. Ammeter will indicate how much energy remains and the amount of time it will take to refuel. A constantly bouncing needle on the ammeter indicates a defective battery and needs to be.