# How Long to Charge a Car Battery at 10 Amps? – Average Time

Written by Edwin Jones / Fact checked by Andrew Wright

When your car battery gets drained after a period of no usage, you may charge it as a solution. In this situation, you might be curious how long to charge a car battery at 10 amps.

## How Long Does It Take to Charge a Car Battery at 10 Amps?

The answer to this question depends on the battery amp hours and charger rating. For a basic formula, you can divide the former by the latter to know how long a full charge takes.

For instance, if you are using a battery charger 12V 10 amp model, a 40 amps hours power bank will only take 4 hours to become full.

This also means that a small car battery rated at 20 amps can reach its capacity within two hours.

However, this estimate may change due to factors such as the ones below.

## Other Factors Affecting the Charging Time of the Battery

### 1. Battery State of Charge

The charging time above is only recommended for a flat or empty battery. It should be reduced if the battery has some remaining power.

You can determine the state of charge by getting the battery’s actual voltage. When the voltage is 12.7V, it means the battery is full. Meanwhile, 12.4V is 75%; 12.2V is 50%; 12V is 25%; and anything under 11.9V is considered empty.

### 2. Battery Temperature

Batteries accept current the best when their surrounding environment is 25℃ or 77℉. Hence, extreme heat or cold will affect the charging time.

Moreover, charging stations or devices will lower the current they supply if the battery overheats. In this case, your power bank will take longer to reach full capacity.

Tip

If your battery can’t hold a charge, you can perform a few troubleshooting measures such as cleaning its terminals, adding battery fluid if needed, and charging it with a trickle charger rated 6 amps or lower for 24 hours. For more this way, check it out here to learn more average time to charge a car battery at 6 Amps and the affecting factors.

However, after conducting these measures and the battery still remains dead, it’s time to let go of it.

## FAQs

Is it Safe to Charge a Car Battery at 10 Amps?

Yes, powering a car battery with a 10 amp charger is definitely safe.

What is unsafe is using low-quality chargers with a higher rating, such as a 30 amps fast charger. These devices may send too much current to the battery, which can overheat and even kill it.

How Long Can I Leave a Battery Charger on at 10 Amps?

You can use this formula to calculate the charging duration:

\text{Charger time} = \frac{\text{Battery Ah}}{0.8 \times \text{Charging amps}}

Since car batteries often have cold cranking amps (CCA) listed instead of amp hours, you can convert the CCA to Ah with some basic math:

\text{Ah} = \frac{\text{CCA}}{7.25}

For example, let’s say you use a 10 amp charger to power a car battery rated at 50 amps. Assuming 100% efficiency, it will take approximately five hours for the battery to go from empty to full.

However, charging is often inefficient, which is why we’ll divide the battery Ah by 0.8; in this case, you will need to wait 6.25 hours for the charging to finish.

On the other hand, if the battery is 50% discharged, it will take 3.125 hours to become full.

Can You Leave a 10 Amp Battery Charger on All Night?

Powering a battery with a 12 volt charger rated 10 amps will take more or less five hours. In this case, overnight charging may damage the battery.

However, some intelligent devices, such as Battery Tender 10 amp rapid charger, will adjust their output depending on the unit they’re serving, so you may use them overnight.

To know if your charger has a feature like this, it would be best to check its instructions manual.

Should I Charge My Battery at 2 or 10 Amps?

Charging a 12V battery at 2 amps may take five times longer than charging at 10 amps. As a result, 10 amp chargers are preferable if you need to use the car soon.

However, a battery tender with a rating of 2 or 4 amps is beneficial if you need to charge your power bank overnight or often forget to unplug your charger.

## Conclusion

Knowing how long to charge a car battery at 10 amps is very beneficial. You can avoid overcharging your vehicle, which is the main cause of damage to its power unit.

If there’s no time for the battery charger to power car amp to full capacity, drivers can rely on the alternator to complete the charging process.