How long does it take to charge your car battery

The further a battery is discharged, the longer it will take to recharge. Usually, it takes several hours to effectively recharge a battery.   

If a battery is almost completely discharged, it can take up to 12 hours or more to recharge. If the battery becomes hot to the touch while recharging, then immediately stop charging. Follow these steps when recharging a battery.

Step 1: Determine how long to recharge a battery by calculating how much capacity your battery has. For example, an Interstate battery with the part number MT-34 has 120 minutes reserve capacity (RC). In order to calculate the amount of amp-hours in a battery, multiply the reserve capacity by 0.6. In the case of a MT-34, 120 minutes RC x 0.6 = about 72 amp-hours (at a 20-hour rate). 

Step 3: Charge the battery at a 10-amp rate. Take the amount of amp-hours needed by the battery and divide it by 10 amps. Using the example above, it would take around 4.5 hours to recharge that battery. (The best charger to use to charge a car battery is a 3-stage automatic 12 volt/10 amp charger.) The charger doesn't really output the entire 10 amps during the charge cycle because it automatically limits the voltage and the amperage during the charge cycle. You may actually only see about half the output over the time period that you are actually charging the battery. For that reason, it can easily take nine hours or more to fully recharge the battery. Even after nine hours, because of the reduced voltage, the battery may require more charging to get it 100% charged.

Step 4: Use a voltmeter or check the battery cells with a hydrometer to make sure the battery is fully charged.

How do you know the best method to charge your battery? We've outlined the difference between a slow charge and a fast charge for you.

Slow charge
It is best to slow charge the battery. Slow charging rates vary depending on the battery's type and capacity. However, when charging an automotive battery, 10 amps or less is considered a slow charge, while 20 amps or above is generally considered a fast charge. 

Fast charge
Repeated fast charges on a battery may overcharge a battery and reduce service life.

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Generally, it should take about 1 hour to charge a car battery at 50 amps. However, it may take longer if your charger isn't compatible with the battery or if there's some underlying defect with the battery itself. In those instances, it could take up to 5 hours.

Better understanding a battery Amp Hour

All car batteries have what's known as an "Amp hour." This is a rating used to tell drivers how much amperage the battery can offer for precisely one hour. This rating influences the battery's voltage delivery, potential power, and runtime.

Therefore, a battery with 1 Ah can continuously provide a current of 1 amp for exactly 1 hour. It could also provide a current of 2 amps for 30 minutes.  

Determining charge duration

Determining charge duration comes down to a simple formula. You simply take the reserve capacity of your battery and multiply it by 0.6. Reserve capacity is measured in minutes, so you should end up with a good estimate for how long your car needs to be at full capacity once again.

Different amp chargers are out there. Each one charges car batteries at different rates. Naturally, the higher the number on your amp charger, the faster your battery charges.

For the following examples, let's assume your battery has a reserve capacity of 100 minutes. In each instance, you multiply 100 by 0.6, which gives you 60 amp hours.  

Using 2 amps

If your battery has 60 amp hours, then a 2 amp charger requires 30 hours to fully charge your battery. To determine this, you just divide the number of amps by the amp hours.

Using 4 amps

When you use a 4 amp charger, it would take you 15 hours to fully charge a battery with 60 amp hours.

Using 10 amps

A 10 amp charger would fully charge a battery in 6 hours.

Using 12 amps

A 12 amp charger fully charges car batteries in 5 hours.

Using 50 amps

A 50 amp charger can get your car back on the road in no time. It would only take 1.2 hours for your battery to be fully charged once again.

Charging at 50 amps is fast, but stay safe!

A 50 amp charger sounds great. But you should be wary. At that rate, there's a risk of overheating the battery.

Higher amps means a faster charge. Problems are more likely to arise if you leave the charger connected long after the battery is fully charged. No matter which charger you use, you should always promptly remove it once the battery has a full charge again.

You can avoid this danger by sticking with a slower charger. A 10 or 12 amp charger gets the job done safely in a reasonable amount of time.

If the battery won't hold a charge, it's time to replace

Something strange may occur when you attempt to charge your car battery. You may realize the battery doesn't hold a charge. At this point, you're better off replacing the old battery with a new one.

There are some key steps to replacing a car battery safely.

1. While wearing gloves, remove the negative cable from the negative terminal. This is indicated with a minus (-) sign.

1. Next, take the positive cable off of the positive terminal. This is indicated with a plus (+) sign.

1. Loosen the connectors and fasteners holding the battery in place.

1. Lift the battery out. Some car batteries weigh as much as 50 pounds, so be careful as you do this.

If you have all the safety supplies you need, then it typically takes about 15 minutes to do all this. In the event you don't feel comfortable doing this, you can take your car to an auto shop to get it done. The price to remove and replace a car battery usually ranges between $110 and $220.

How to tell when it's my battery or another car issue?

There's no need to replace the battery if there's something else causing issues in your vehicle. This is why it's critical to get your car inspected by a professional annually.

The right insurance can help you out if you're in a pinch. If you find yourself on the side of the road with a dead car, then insurance can provide roadside assistance. You can be on your way to the nearest auto shop in no time.

The right insurance policy also covers critical repairs. While it doesn't cover normal wear and tear, it can protect you if something is damaged in an accident. But if you notice any of the following signs, then the culprit is likely a faulty battery.

• Engine slow to start

• Dim headlights and dashboard lights

• Illuminated check engine light

• Corroded connectors

• Misshapen battery case

When the time arises, is my insurance going to be enough?

When it comes to car insurance, there are several factors to consider beyond monthly cost. A policy that covers you when you need it, has a low deductible, and offers several discounts can be hard to find - which is why we've done the work for you.

Get instant quotes tailored to your needs - fill out our short form, today!

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