How Many Amps To Charge A Car Battery?

Key Points:

  • The amps at which you choose to charge your car battery impacts the battery and its health.
  • The charger rating and the battery ratings both play a role in the decision making.
  • To be in the safe zone it is advised to charge at 4 to 7.5 amps.

While connecting a car battery to a charger is pretty simple, there are a few things to bear in mind to guarantee that your battery is not harmed and that you get the most out of its potential lifespan. So, how many amps to charge a car battery?

The safest and most effective way to charge a car battery is at 4 to 7.5 amps. This range of charging amps will allow the battery to be fully charged overnight without fear of overcharging. For the greatest results, use a three-stage or smart charger.

This is the quick and simple answer. However, other significant questions involving batteries, such as how to properly charge them, how to maintain them, and so on, may emerge. Throughout this article, I’ll try to cover some of the most prevalent questions and give comprehensive and detailed answers.

How Many Amps Should Your Car Battery Be Charged at?

Nearly all automotive batteries are lead-acid at present moment. It’s possible they’re flooded lead-acid, in which case you may remove the lid to inspect the electrolyte within.

Often time they might be sealed, making it impossible to inspect the internal electrolyte. In any case, they’ll be classified as lead-acid.

So, if you are wondering how many amps to charge a car battery, a charger with an amp rating of one-tenth or less of a lead-acid battery’s total amp-hour capacity is recommended.

If you knew your battery was rated at 100 amp hours, for example, you’d want to choose a charger rated at 10 amps or fewer.

A 5-amp charger would suffice if your battery was rated for 50 amp hours.

A 5 to 7.5-amp charger would be suitable for most automobile batteries, which range between 50 and 70 amp-hours.

Keeping your charger’s amp rating in this range allows your battery to fully charge overnight while also being soft enough on it to give it a thorough charge while avoiding overheating and electrolyte loss.

The issue with automobile batteries is that they are rarely labeled with amp hours on the sticker. A reserve capacity, cranking amps, or cold-cranking amps are all common terms.

The conversion of Cranking Amps or Reserve Capacity to Amp-Hours is not straightforward. It’s the same of claiming that your automobile can accelerate from 0 to 60 miles per hour in 6 seconds and then attempting to calculate how many miles per gallon it would get at 60 miles per hour. For various reasons, they’re all distinct measurements.

The most appropriate charger for your car’s battery is a 4 to 7.5-amp smart charger that will enter a float or maintenance mode after it is finished charging. Chargers in this range will often have amp ratings of four, five, six, and seven and a half.

How Do Amps Affect the Battery Charge?

When it comes to charging your automobile battery, amps do important. The majority of automobile batteries are 12-volts, as shown on the battery’s tag. Just because you have a 12-volt charger in your hand doesn’t mean it’ll work with your battery. The amps supplied by the charger (the current that is pressured by the voltage) may either safely charge or completely kill your battery.

When charging a battery, amps are important because if you use a charger with an amp rating more than 10% of your battery’s total amp-hour capacity, you risk an inefficient charge, excessive heat build-up, electrolyte loss, or worse.

For example, if you had a 50-amp hour battery and a 5-amp charger, it would take around 10 to 12 hours to fully charge the battery from a dead condition.

What occurs is that the extra voltage begins to boil the electrolyte within the battery, a process known as electrolysis. During the boiling process, excess heat is generated, and the electrolyte is ejected from the battery.

Sealed lead-acid batteries can recombine evaporated electrolytes up to a certain point, but if that threshold is exceeded, the battery will release the evaporated electrolyte to depressurize.

When electrolyte evaporates and is not supplied quickly enough, the lead plates inside the battery are exposed to air and suffer instant and irreversible oxidation damage which can and does negatively affect the battery health.

So, when it comes to charging your automobile battery, amps do important. Keep your charger between 2 and 7.5 amps (no more than 10-amps), and I recommend something on the higher end of that range to guarantee that your battery gets charged overnight.

Is It Necessary to Unplug My Car Battery Before Charging It?

If you’re using a microprocessor-controlled smart charger, you don’t need to disconnect your car battery before charging it. These chargers are clever enough to ensure that your vehicle’s electronics are not harmed.

According to user feedback and experience, utilizing a smart charger to charge a car battery while it is attached has never been a problem.

It did mention, though, that if you have an older charger that isn’t microprocessor-controlled, you should be cautious and unplug your battery before charging.

Some battery chargers include up to three separate amperage ratings on the label, such as “2/10/50.” The 2 and 10 are the true “charging” amps, while the 50 is only a helper to aid a weak battery in starting an engine. It should be utilized as a “boost” rather than a charge.

How Long Does It Take to Recharge The Battery After Starting The Engine?

It doesn’t take a long time to be honest. This isn’t difficult to estimate. Cold cranking amps (CCA) are measured in 12-volt automobile batteries, and the one I use has 800 CCA.

Let’s say, for the sake of argument, that the automobile requires 800 amps to start. I have three automobiles that are 17 years old, 14 years old, and 22 years old, and they all start in less than 3 seconds, but let’s suppose 10 seconds to be conservative.

So, 10 seconds multiplied by 800 amps is 8000 amp-seconds (or 2.2 amp-hours for you physicists). This will be changed in 99 seconds if the alternator is supplying 80 amps.

A more correct figure would be 200 amps for 3 seconds, followed by an 8-second replacement.

This ignores the reality that a nearly-full battery won’t be able to handle the entire 80 amps.

A good graphic in Linden’s Battery Handbook demonstrates that a battery nearing 100% charge charged at 14.4V will tolerate around 9 Amps per 100AH of battery capacity.

The charge will return in roughly 83 seconds utilizing the 600 Amp-second casing and an 80AH battery.

Is It Possible to Use a Vehicle Battery Charger as a Power Source?

Older automobile battery chargers can be used as power sources, but modern ones come with a safety function. The charger will not give electricity until the presence of a battery on the leads is detected.

To put it another way, in order for the charger to turn on, some external voltage must be applied to the leads.

As you can see, this avoids high-current sparks from the alligator clips shorting, but it also prohibits you from charging a completely dead battery or utilizing the charger as a power supply to power a vehicle audio in your home.


Throughout this article I have tried to thoroughly discuss the questions that might arise in one’s mind regarding charging car batteries including how many amps to charge a car battery.

I have also brought up explanations as to how amps affect the charge battery while charging them and what the adverse effects of using a non-compatible amp could be on your battery.

I hope that this article has helped answer most of your questions regarding car batteries and their charging mechanism. Thank you.

Leave a Comment

Your email address will not be published.