Car batteries are generally self-sufficient when installed in a car, thanks to the alternator. However, unfortunate situations may prevent the car battery from fully charging. A charger is a good solution to charge the battery while the vehicle is not in use.
A basic car charger is usually 2 amps, and how long to charge a car battery at 2 amps will depend on the amp-hour rating of the battery, but it may charge at least 24 hours.
Table of Contents
Charging a Car Battery
Two major factors are looked at when determining the time it would take to charge a car battery:
- The capacity of the battery in amp-hours
- The battery charger rating
The amp-hour rating shows how many amps a 12 volt battery can give at a certain time. For example, a 50 amp battery can give 50 amps in one hour, or 25 amps in 2 hours, or 10 amps in 5 hours.
The higher the amp-hour rating, the larger the capacity, and thus, the longer the battery will charge, so expect longer times to charge truck battery capacities than a sedan battery.
We can express amp-hour ratings (Ah) with this relation:
We can re-arrange the expression above to know how long does it take to charge the car battery:
For example, if the car battery charger is rated at 2 amps, then our 50 amp-hour battery will have a charger time of:
This means it will take 25 hours for a 2 amp car charger to fully charge a 50 amp-hour battery. Remember that it would take less if the battery is not fully discharged.
We can summarize the estimated time in a table for easy viewing. We displayed the time it would take for a 2 amp charger to charge certain fully discharged batteries with the following amp-hour ratings as well as other car battery charger amps.
| Amp-hour rating | Charging time in hours | |||||
| At 2 amps | At 4 amps | At 6 amps | At 10 amps | At 30 amps | At 40 amps | |
| 50 | 25 | 12.5 | 8.33 | 5 | 1.67 | 1.25 |
| 60 | 30 | 15 | 10 | 6 | 2 | 1.5 |
| 70 | 35 | 17.5 | 11.67 | 7 | 2.33 | 1.75 |
| 80 | 40 | 20 | 13.33 | 8 | 2.67 | 2 |
| 90 | 45 | 22.5 | 15 | 9 | 3 | 2.25 |
| 100 | 50 | 25 | 16.67 | 10 | 3.33 | 2.5 |
A battery charging time calculator is also available online.
However, take note that some things might affect how fast the battery might get fully charged, whether you are using a charger rated at 2 amps or 6 amps. These include a dead cell in the battery or a sulfated battery.
Also, the voltage of the battery is lower, so it only draws less car battery amps than at 12 volts.
Unfortunately, using high amp-rated chargers or fast chargers for a fully discharged lead acid battery may produce a lot of heat due to the internal resistance in the battery, and may affect the battery’s lifespan. Thus, it’s best to use these 40 amp chargers for 15-30 minutes then shift to a lower amp like a 5-10 amp charger.
Frequently Asked Questions
Is it better to charge a battery at 2 amps or 10 amps?
It’s OK to charge at 2 or 10 amps, but you can recharge faster using a 10 amp charger. 2 amp chargers are usually known as 24 hours chargers are used by those who want to take the charging process slowly. You can even charge with a 1 amp charger but it would take longer.
How long should you leave a car running to charge the battery?
Normally, it takes around half an hour to fully recharge a battery with the alternator at highway speeds. You can charge the battery a bit to get the car started and charge it with alternator to full charge.
Can you overcharge a car battery at 2 amps?
You can overcharge a car battery at any car battery charger amp rating. The battery might just die or might explode due to the buildup of gas in the battery.
Conclusion
How long to charge a car battery at 2 amps will depend on the capacity of the battery. Usually, it could take at least 24 hours to charge a fully discharged 48 amp-hour battery, but it could take longer for larger capacities. It could also take less time if the battery is not fully discharged.
Of course, higher charger ratings will give faster charging times, but limit the rating to 10 amps. Using these chargers, even the 2 amp chargers, must be thought of thoroughly to ensure your battery works for as long as it needs to.
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I am Edwin Jones, in charge of designing content for Galvinpower. I aspire to use my experiences in marketing to create reliable and necessary information to help our readers. It has been fun to work with Andrew and apply his incredible knowledge to our content.