How to Read a Battery Charger Gauge

As an Amazon Associate I earn from qualifying purchases. Contact us if you have any questions :)

I’m gonna be honest with you. There’s no direct answer on how to read a battery charger gauge.

The answer will depend on whether you have either a manual or modern microprocessor-controlled car battery charger. The latter is decidedly more expensive, but it is fully automatic and compatible with all types of AGM automotive, marine, industrial, or deep cycle battery.

Read a Battery Charger

However, the basic principle remains the same. Some battery chargers may come with manual dials and needles to indicate the state of charge. On the other hand, fully-automatic battery chargers will have LCD display screens, making it easier to read the charging state.

How do I read the battery charging gauge?

If you’re storing a car battery for long term or over the winter months, you’ll want to charge it and monitor the levels. This is where the battery charge gauge becomes useful.

The best answer is to read the operating manual of the battery charger.

It will give you a complete synopsis on how to operate the product. But if you’re working with an older charger equipped with a needle gauge, it is fairly easy to read the state of charging.

Upon powering up the charger (which is hooked up to the donor battery), the needle will first move to around 6 amps. This is especially true if the battery is completely flat. After 10 to 15 minutes, the needle will slowly move left or downwards to 4 amps and eventually 2 amps. If the needle is consistently pointed at 2 amps, it means the battery is achieving a fully charged state.

Read more about Car Battery Amps.

But if you have a car battery charger with two needle gauges, the same principle holds true except for the second gauge. In most cases, the first gauge is the preferred charging rate (which can be manually adjusted from 2, 4, to 6 amps) while the second is the charging rate. Even if you switch to the lowest 2 amp setting, the second needle will first move to 6 amps upon starting the charging process. The needle will slowly fall to 4 amps and eventually settle to 2 amps as the battery is juiced up.

How to Connect a Car Battery Charger and read the gauge

In this section, it doesn’t matter if you have a manual or automatic charger. The process of hooking up the charger to the receiving battery is the same.

  1. It’s your choice if you decide to remove the battery from the hood of the vehicle or not. You can achieve the same results in doing both, although it is important to remember not to place the battery in a cemented floor, especially when charging the battery. Place it on top of a strong wooden desk, or simply place a thick layer of carton between the car battery and cemented floor.
  2. Remove the battery clamps from the battery terminals. Always remove the negative (-) terminals first before the positive (+). Remember: red is for positive, and black is for negative. If you’re still unsure, take a closer look at the battery. It will usually reveal which is the positive and negative terminal.
  3. Connect the charging clamps. First, connect the positive (+) or red clamp. The next step is to connect the negative (-) black clamp to a metal part in the engine bay. This helps to achieve a solid ground for faster, safer, and more efficient charging.
  4. Connect the power cable of the charger to an electrical outlet and turn it ON. Depending on the type of charger, the charging process will commence immediately. You can check or read the needle gauge to view the charging current applied to the battery.
  5. You’re done. Most automatic or semi-automatic chargers will stop applying current once the battery is fully charged. If you have a manual battery charger, the battery is nearing or entering a fully-charged state if the needle is constantly pointed at 2 amps.

What is the ideal charging amperage?

Again, the answer depends on the type of battery. In terms of car batteries, a charging rate of 2 amps is the norm. But if you’re working with a weak or flat battery, cranking up the charging rate to 4 amps or 6 amps will speed up the process, but only for short periods.

If your battery is going bad, check out out best rated car batteries guide.

How long does it take to charge a car battery?

I’m sorry to disappoint you, but the answer will again depend on state of discharge and size of the battery (A Group 31 is larger than a Group 34 battery for example). Most automotive and commercial applications, a 48 amp hour battery is the norm. So if the battery is completely flat, it will take around 24 hours to achieve a full charge with a 2 amp battery charger.

Cranking up the charging rate to 4 amps will juice up the aforementioned flat battery in 12 hours, or half the time. And if applicable, a 6 amp charging rate will complete the job in around 6 hours, but this is not applicable for most car batteries.

Are computer-controlled or fully automatic battery chargers better?

It’s not that modern car battery chargers are much better than conventional manual chargers. Both products are designed to do the same job, and both are great in terms of the intended purpose.

But the difference is measured by safety and ease of use. Automatic battery chargers have an internal brain controlled by state-of-the-art microprocessors. The charger can automatically select the perfect charging settings by adjusting the voltage and charge current. This allows the charger to maintain and protect the health of the battery, whether you have an AGM, gel cell, deep-cycle, marine, or conventional car battery.

However, reading an automatic battery charger is different from a manual charger. Since most automatic chargers are equipped with various settings, the value you’re reading in the LCD screen might vary depending on the preferred settings.

When using an automatic battery charger, I have a habit of switching to the battery percentage setting, similar to a smartphone or tablet. This negates the complexity of determining whether the charger is set to 2 or 6 amps. It simply states the battery is at 40% or 50% capacity. The charger automatically applies the proper charge current depending on information collected from the battery. It can even enter a multi-phase charging process to make sure all the energy is absorbed by the battery.


Hit a roadblock? Let us connect you with a pro.

If you’re having trouble with your car, it might be time to talk to an expert. Scanner Answers is proud to partner with RepairPal to help you find the best deals on car repair in your area. RepairPal mechanics specialize in offering high quality work at guaranteed fair prices. Find a Repair Shop or speak with an expert now Call (877) 314-1060