How Long to Charge a 12V Car Battery at 6 Amps?

There are 12V battery chargers that can charge at different amp rates and sometimes it is not clear the implications on charging time or even when you should select a particular charge rate – for example, the 6 amp charger.

If this is you then read on for estimated charge times with a 6 amp, 12V battery charger, when to use it, and how to get the best results with it.

Charging Time for a 12V Car Battery at 6 amps

A 6 amp charger takes about 6 – 10 hours* to charge a 45 Ah car battery.

How long it takes the battery to charge fully depends on the extent to which the battery is depleted.

Going off this then a partially charged battery will take a much shorter time than one that’s been drained more.

*Note, this charge time estimate assumes that the battery is only discharged to 50% of its capacity.

Check the battery charger owner manual – you can usually find the estimated charging time for different battery capacities there.

Ultimately, how long the car battery takes to charge depends on several variables but the main ones are:

  • The battery capacity (Ah). The bigger the capacity (Ah), the longer the charging time
  • The extent to which the battery has been drained. A deeply drained battery will take a longer time to fully charge

Should you Leave a 6 amp Charger Connected to Car Battery?

While some car battery manufacturers suggest that you can leave the charger connected and unattended while charging the battery, I do not feel comfortable doing so for an extended period such as going away on a vacation.

I would only do so for the duration of the charging – the 6-10 hours and even then, I’ll monitor the battery temperature from time to time, ready to switch it off should it become hot.

Should you decide to leave the charger on the battery unattended for longer then:

  • confirm that indeed the manufacturer recommends leaving the charger unattended
  • check whether it has an automatic shutoff feature to stop charging when the battery is full,
  • The battery is in good condition (no short el al) – has no history of overheating, no signs of bulging and
  • if it is of the capacity and chemistry recommended by the manufacturer.

If it ticks all these boxes then you can consider leaving it unattended and charging a car battery for a long time.

Remember to always consult the battery charger owner manual for what other safety recommendations the manufacturer may have included.

Tips to Charge a 12V Battery Safely & Successfully Using a 6 amp Battery Charger

To get the best charging performance from a 6 amp charger:

1. Check the battery voltage and chemistry. Is it a 6V or 12V battery? Is it an AGM or LiFeP04 (lithium) battery?

Confirm the type of battery and its voltage and make sure the charge is designed to set your battery type and is set to charge your battery’s chemistry and voltage.

The car battery may be undercharged or overcharged if the wrong battery type is selected!

2. Switch off car accessories to get the battery to charge faster.

The 2 amp battery charger is a slow charger and the charging time will be longer than expected if some car accessories, such as a car radio, navigation systems, or others are switched on while the battery is charging.

3. Check whether the charger has an automatic shut-off feature? Does it adjust the voltage settings depending on the temperature?

Do not leave the battery unattended when charging with a dumb charger, no automatic adjustment of voltage settings depending on battery temperature, and no automatic shut-off when fully charged.

Monitor it and when the indicated charging time (estimated charging time for different battery capacities usually included in battery charger owner manual) has elapsed, switch off the charger.

What is a 6 amp, 12V Battery Charger Best Suited For?

For normal charging of 12V car batteries with a capacity larger than 22Ah!

Make sure it is set to charge for the battery type that matches your battery – whether AGM, GEL, or LiFeP04.

Can a 6 amp Charger Damage a Car Battery?

It could cause damage to the battery. Some of the common pitfalls you should avoid:

  • Make sure that battery capacity is large enough – manufacturers usually recommended larger than 22 Ah
  • Confirm that the setting for the battery type that matches your battery is selected -whether AGM, GEL, or LiFeP04.

I’m also against leaving the charger unattended to charge the battery. The battery can overheat and explode – this is extreme of course.

Prior to this happening, the battery will likely overheat and if you’re periodically checking on it, it is easy to catch this earlier and switch off the charger.


  • Make sure the charger is installed in a place with a good flow of air to avoid overheating and damage to the charger and battery
  • Make sure the battery is charging, i.e the charge has detected it before you leave it unattended
  • Confirm that it is suited to charging batteries of your battery type and capacity. A high-capacity charger can damage a small-capacity battery

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Can You Overcharge a 12V Battery with a 6 amp Charger?

Yes, you can still overcharge a 12V battery with a dumb 6-amp charger with no automatic shutoff when the battery is fully charged.

Make sure it is set to charge for the battery type that matches your battery – whether AGM, GEL, or LiFeP04.

Which one – a 6 amp vs. 2 amp Charger?

If you’ve got a charger that supports both 2 amp and 6 amp charging or both and want to know when to use which charger then this might be helpful.

For normal, reasonably fast charging go for a 6 amp charger.

Make sure that the car battery is more than 22Ah and always confirm that the charger is set to charge for the battery type that matches your battery – whether AGM, GEL, or LiFeP04.

A 2 amp charge rate is generally used to keep the battery topped up.

Make sure it is a well-regarded charger (from the user reviews and that the manufacturer recommends that it is used that way) – not all chargers are built the same!

Final Thoughts

How long it takes to charge a battery at 6 amps mainly depends on how deeply discharged the battery is, its age, and its capacity.

For example, a 6 amp car battery charger will charge a 45Ah car battery discharged to 50% of its capacity in about 6-10 hours.

The actual charging time varies depending on the factors mentioned above.

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