How To Read A Battery Charger Amp Meter

Battery chargers come in various shapes and sizes. The basic information required for charging your battery is uniform and standardized, but high quality battery chargers include a number of safety features that prevent the battery from overcharging as well as provide information on the status and condition of your battery. Safety features include a voltage regulator, LED light and an automatic shutoff feature.

An overcharged battery can be dangerous because it risks causing the battery to explode. The indicators on the battery charger will inform you when the battery is fully charged, as well as allow you to set the time frame for charging the battery, which is why it is necessary to know how to read a battery charger amp meter.

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How Do You Read a Battery Charger Amp Meter

How to connect a battery charger

Okay, now we have to connect the charger to your battery before we start using the ammeter on the battery charger. These steps are simple, but we must take some precautions before doing the process. In the following lines I will guide you step by step to connect your battery charger safely.

Step 1: Make sure that the cells of the battery terminals are clean, as they get dirty very often due to road dirt.

Step 2: Be in a well ventilated area, as batteries have hydrogen gas as it is explosive.

Step 3: Use proper protective equipment such as gloves and some type of eye protection, as batteries contain acid.

Step 4: Make sure that everything in the vehicle is turned off, in case the battery is mounted to the car.

Step 5: Observe and identify the negative (Black) and positive (Red) terminals.

Step 6: Connect the red cable to its similar color on the battery.

Step 7: In this step, when connecting the black wire to its terminal, it will cause a spark, and will emit hydrogen gases that will spread in the air. Because of this, it is advisable to connect the black terminal at a safe distance.

As a suggestion, you can connect a wire of approximately two meters to the negative terminal and connect the black wire to its end.

How To Read A Battery Charger Amp Meter

How To Read A Battery Charger Amp Meter
An amp meter on Schumacher battery charger Source:

Ammeters, also known as ammeters, measure amperage, or the power of electrical current in amperes. As such, these meters essentially act as “flow meters,” reading the battery current of the electrical system under normal conditions.

Automotive ammeters measure the alternator output used by the battery through the heavy gauge wire defeated under the dash. If the system alternator fails, the ammeter also measures the battery discharge. For safety reasons, the current rating of the ammeter must be greater than the maximum alternator output.

Charge Rate

As shown in the figure above, the bottom part, where the small cubes are shown, indicates how much ampere flows between the charger and the battery, this ranges from zero to twelve.

Percent Charged

In the Percent Charged row the needle indicates the percentage of the battery. For example, in the picture above the needle is close to 60%, which indicates that the battery is 60% charged.

The needle should be moving to the left, approaching 100% charge, at or near zero amperes.

Red and Green Triangles

The small red triangle goes from 0 to 2 amps, this indicates the amps flowing in a 2 amp configuration.

The large red triangle shows the amount of amps flowing from the charger to the battery.
As the battery load increases, the flow rate decreases, moving to the left side and into the green area, indicating when the battery is charged, which is about 6 amps.

If all this is complicated, here’s a little analogy.

Imagine you have two buckets connected by a hose. Your charger is a bucket full of water, your battery is the other half of the full bucket and the hose is your cables.

The goal is to get the water from the charger tank to the battery tank. You can use a large hose to do this (10 amp charge rate), but you risk splashing water everywhere, or use a smaller diameter hose to slowly fill the bucket, but it is more controlled (2 amp charge rate) and will not spill or spill any water.

How to tell if a battery charger is being charged

Plugin the charger and turn it on. The indicator light (ammeter) will indicate that the battery is charging. The indicator will show a high charge rate at first, but will gradually drop as the battery charges.

How long does it take to charge a car battery

What should a battery charger read when fully charged?

If the needle sits at around 6 amps on a 12 amp charge setting, that indicates that the battery is fully charged. If you use a 2 amp setting, the needle will settle at the end of the small red triangle.

How long does it take to charge a car battery with a 6 amp charger?

The average car battery has the capacity of 48 amps per hour (amount of current a source can provide in one hour), which means that fully charged, it provides 1amp for 48 hours, 2 amp for 24 hours, 12 amp for 6 hours and so on progressively.

A charger charges on average about 6 amps, so it takes about 12 to 13 hours to provide the 48 amps needed to fully charge a battery.

Problems reading a battery charger indicator

Battery charger needle does not move

  • The battery charge is too low: The usual chargers are not effective with a completely empty battery. Even today’s trickle chargers with maintenance mode may not have any problems. But there is a way around it, let’s see how.
  1. You can put another battery that has a good charge in parallel with the defective battery.
  2. Connect the two batteries with connecting cables: positive to positive and negative to negative.
  3. The same as when starting the car.
  4. Now connect the charger and you are done.
  • Charger ammeter failure – To troubleshoot the charger malfunction, connect a working battery. If it shows the same problem, it is most likely a faulty battery charger.
  • Dirty battery terminals: The vehicle battery may be covered with a large amount of dirt and the battery terminals may be corroded, if so, clean them and try again.
  • Ammeter needle is stuck: Mechanical needles can get stuck, especially if the charger is old. Gently tap the meter to see if it moves.
  • Your AC outlet is defective: For the charger to work, the AC outlet must be in good condition. You can check this by plugging in another electrical object, such as a light bulb.

Battery charger needle jumps

  • Poor connection: Charger clips are not connected properly or are in poor condition,
  • Defective battery: Battery with internal defects or completely discharged.


The vast majority of people do not know how to read the charger meter. We hope this guide has given you an idea of the usefulness of the meter.

Being able to read your charger’s ammeter is useful in many ways. Not only can it show the status of your battery, it can also help diagnose charging problems.

So the next time you’re charging your battery, take a look at the charger’s ammeter.

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