How Long to Charge a 12V Car Battery at 2 Amps?

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There’re car battery chargers that charge at various charging rates from as low as 1 amp up to 40 amp or even higher. There’re obviously implications for using each charge rate.

With a 2 amp charger for example, how long does it take to charge a car battery? What else should you keep in mind to charge one safely?

Read on for indicative charging times for a 12V car battery with a 2 amp charger, when to use it, and how to use it safely to avoid damage to the battery.

Charging Time for a 12V Car Battery at 2 amps

As a rough guide, a 2 amp charger takes about 15 hours to charge a 40 Ah car battery. A bigger-capacity battery will take longer to charge.

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.

A dead battery may fail to charge or take a longer time to charge the battery especially if the battery voltage is as low as 1 volt or less.

Some chargers like the NOCO Genius have a “force mode” to charge batteries whose voltage is extremely low!

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

  • The battery capacity (Ah). The larger it is the longer the charging time
  • To what extent the battery has been drained or not. A deeply drained battery will take a longer time to fully charge

Should you Leave a 2 amp Charger Connected to Car Battery?

Leaving the battery charger connected to the battery generally depends on:

  • quality of the charger and
  • whether it has an automatic shutoff feature,
  • The battery is in good condition (no short el al) and
  • if it is of the capacity and chemistry recommended by the manufacturer.

If it ticks all these boxes then you can usually leave it unattended charging a car battery for a long time.

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 2 amp Battery Charger

Even though the 2 amp charger is a low amp charger, if you want to get the best performance from it, you should:

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. Does the charger have 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 2 amp, 12V Battery Charger Best Suited For?

Not one for fast charging!

Personally, I would only use a 2 amp charger as a trickle charger or battery maintainer unless I plan to use it to charge a 12Ah battery. This one can be charged in about 4-5 hours.

Larger capacity (Ah) batteries such a long time to charge a car battery! 15 hours for a 40Ah Car battery and even then when it has been discharged to 50% of its capacity.

Can a 2 amp Charger Damage a Car Battery?

If it is a good quality charger with automatic shutoff when the battery is fully charged then yes I could leave it charging overnight unattended for even longer without fear of damage.

Do not compromise – make sure it is a reputable charger or else the chances of damage to the battery are high!

This is a personal decision though because even with some manufacturer safety claims, there have been cases of batteries suffering damage from overcharging!

Follow these tips for additional safety:

  • 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 Using a 2 amp Charger?

Yes, you can still overcharge a 12V battery with a dumb 2-amp charger. Use a good quality 2 amp smart battery charger and maintainer suited to your battery type (AGM, wet, or Lithium).

What amps to Charge a Car Battery at?

The best advice here is to check the recommended charging current by the manufacturer.

Some battery chemistries such as LiFeP04 can withstand faster charging compared to an AGM battery with the same capacity.

That said, whenever in doubt, to play it safe, use the general rule of thumb of not exceeding 10% of the battery’s capacity.

A 100Ah battery would be charged at 10 amps – using a 10 amp charger as an example.

Using a lower amp charger, say a 2 amp charge instead works too but further extends the time to charge which may not work for you!

Final Thoughts

How long it takes to charge a battery at 2 amps mainly depends on how deeply discharged the battery is, its age, and its capacity.

For example, a 2 amp car battery charger will charge a 40Ah car battery discharged to 50% of its capacity in about 15 hours.

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

Only use a good quality charger with automatic shutoff that is suited to charge your battery capacity, chemistry, and voltage to charge your 12V battery.

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