If you’re charging a battery, it is important to know how to read a battery charger amp meter or ammeter so that you will know exactly how many amps are flowing into the battery. But before knowing ways to check an amp meter when you install the battery, lets, first get to know what an amp meter is and what it does.

What is an amp meter

An amp meter is an instrument that measures the electric current flowing into an electrical device or, in this case, a battery. The term amp meter is derived from ampere, the standard unit of measurement for electric current.

The amp meter in a battery charger displays how much electric current is being outputted by the battery charger to the battery.

You should realize that an amp meter only measures electric current and not voltage. These two are not the same or are they interchangeable. Voltage is a measurable expression of the possible difference in charge bounded by two points in an electric circuit. It can be considered as the energy enclosed within an electric field or circuit at a single point. While current is the amount of electric charge that flows at any given point on an electric circuit.

One way of understanding the difference between current and voltage is to compare electricity passing through a wire with water passing through a water hose. In this comparison, voltage is the water pressure while current is the rate of the flow of water. When you change one, the other changes also, but they are not identical.

How to Connect the Battery Charger

Before you can read the amp meter of the battery charger, you need to connect the charger to the battery first. Remember, when working with batteries it is best to wear safety gloves and goggles.

Here are the steps for connecting the charger.

Step 1 – Disconnect the battery from the car

When disconnecting the car battery, make sure that your engine is not running, and the key is not in the ignition. Now, locate the battery under the front hood of the car. With a socket wrench, twist the nut of the battery’s terminal (negative terminal first) counterclockwise to loosen it. When the nuts are loose enough, pull off the negative connector from the battery. Repeat the process with the positive terminal.

Step 2 – Connecting the charger to the battery

Before connecting the charger to the battery, make sure first that the charger is off, the electrolyte level is good. If it isn’t, top it off with distilled water. Also make sure that the battery posts are clean.

When you’re ready, connect the positive clip of the charger’s cable to the positive post or terminal of the battery. The positive clip of the cable is usually red while the positive post of the battery has a “+” sign. Repeat the process for the negative post. The negative clip of the cable of the charger is black.

Ways to read a battery charger amp meter

Once you have connected the charger to the battery, you’re ready to charge the battery and read the amp meter.

Plug the battery charger and switch it on. When the charger is switched on the needle of the meter moves to the desired amps, say ten amps. As the battery continues to charge, the needle moves down. When the needle has dropped to almost half of the desired amp, it means that the battery is fully charged.

The amp meter has two red areas. They show the charge rate you have chosen at the start of charging. On the far right, there is a red area that is for the higher charge rate amperage. The red area on the left side of the amp meter specifies rates for the 2-amp position. When you start charging, the needle moves to the right red area, but when the battery becomes charged the needle drops going to the left in the vicinity of the large red area.

If there are two needles in the amp meter, learn to distinguish which is which. The needle that points to the desired amp when switched on is the needle that will tell you how much amps is being put out by the charger.

The second needle will tell you the amount of charge the battery has. When the needles are one on top of the other, the amp meter is telling you that the battery is fully charged.

When there is a short circuit in the battery being charged, the amp meter will indicate that the charger is releasing maximum current and that the battery is largely discharged. When 5 to 10 minutes has elapsed, and the needle is still not moving to approach the lower amperage, discontinue charging. If you have a voltmeter, try reading the battery voltage, and when the reaction is below 12 volts you might have a defective battery that needs servicing or replacing,

But if the voltage reading is more than 12 volts, you can continue charging. However, if 15-20 minutes have passed and the amp meter needle still remains stationary and has not dropped to lower amperage, give the voltage test another try. If the reading is the same as before, then you have a problem. The battery is defective and would have to be serviced or replaced.

Digital Amp Meters

Some of the more advanced battery chargers have digital ammeters. Digital ammeters do not have moving parts. A circuit like a dual slope integrator is used to change a measured analog reading to its digital equivalent. The accuracy of a lot of digital ammeters is better than 0.1%.

Digital battery charger amp meters are easy to read since the amp reading is displayed in the LED display. But many of these digital ammeters also work as a voltmeter or as a multimeter so much so that it becomes confusing. To be sure that it is the amp output that you are reading set the device correctly. Search the read option until you find the readout that says amp output.


How you read a battery charger amp meter does not need genius, as long as you know what you want to know and how the amp meter works. The analog amp meter has a needle that will indicate the amp output while a digital amp meter has the numbers displayed.