There are a few components of a car that a car owner should have knowledge about. The knowledge about them is important not only for troubleshooting and replacement purposes but also for using those components in combination with other electronic gadgets. There are many important components of a car, and a battery is critical.
The battery plays its part in starting the car engine and powering lights, multimedia systems, and air conditioner. Most car owners may know that their car battery belongs to the 12 volts category, but not many of them are aware of car battery ampere ratings. It is essential to know the parameter before charging your battery. In this article, we will explain what ampere rating is and how to figure it out for your car battery.
What is the Ampere Rating of a Car Battery?
The amp rating of a car battery represents the current storage capacity of the battery. The larger the battery, the higher the ampere rating. The amp rating of a car battery varies from 550A to 1000A. Note that the amp rating is different from the amp hour rating that most batteries come labeled with.
The amp rating of a car battery depends on several factors starting from internal chemistry to reserve capacity. Therefore, you have to understand the specifications of a car battery before understanding and measuring the amp rating for a car battery.
Specifications Of Car Battery –
Here are some of the important specifications of a car battery that you should be aware of.
Chemistry – The chemistry of a car battery refers to the type of battery it is. Most car batteries are lead-acid batteries, but flooded lead-acid batteries are getting replaced by AGM(Absorbent Glass Mat) and SLA(Sealed Lead Acid) batteries. AGM and SLA batteries are better in terms of vibration resistance, less maintenance, and spill-proof.
Capacity – The capacity of a battery is measured in Amp Hour. It represents how many amps of charge the battery can supply for hours until its voltage reaches the cut-off voltage. Generally, the cut-off voltage is 10.5V for a lead-acid battery.
Cranking Amps – It is the maximum current that a fully charged battery can supply for 30 seconds without any voltage drop. It is a parameter for measuring the strength of the battery. The cold and the hot cranking amps show how the battery will perform in cold and hot weather conditions.
Pulse Hot Cranking Amps – It is the maximum current that a new battery offers for 5 seconds after it starts operating. It is used to measure the starting strength of a battery.
Maximum Charging Current – It is the maximum allowed current that you can use to charge the battery safely.
What is an Amp-Hour Chart of a Car Battery?
The amp-hour chart is associated with batteries for marine vehicles, cars, as well as campsites. The amp-hour chart is actually a measurement of the capacity of the battery. We have already discussed capacity under the specifications of a car battery. The amp hours actually measure how long a car battery will last. Therefore, if the amp-hour of a car battery shows 100Ah, it means the battery can deliver 5 amps for 20 hours. Similarly, it can deliver 10 amps for 10 hours and so on.
The internal chemistry of a battery has a huge impact on the amp-hour chat of a car battery. Here is an amp-hour chart that shows the difference between a flooded battery and an AGM battery. You can clearly see how efficient the AGM battery is over the over-flooded battery.
How Many Amps and Hours are Needed to Charge a Car Battery?
Normally, a car battery charger sends 2 amps of power per hour to the battery. Generally, it takes around 24 hours to charge a battery. You may consider this to be slow but slowing charging of a car battery is always preferred because it prevents overcharging and damaging the battery and reducing its lifespan.
However, you will find fast-charging options such as a 10-amp charger that can charge your battery in a few hours. However, you have to ensure that you do not overcharge it and hence, it will require frequent monitoring during charging hours.
In order to determine how many amps are required to charge a car battery, you have to subtract the current capacity of the battery from its total capacity. Once you know the total amps required, you can divide the total amps by the amp rating of the charger and you will know how many hours of charging your battery needs.
Charging hours required = (total capacity – current capacity)/ amp rating of the charger.
How Do You Measure Car Battery Amps?
If you do not know the total capacity and the current capacity of your car battery, you cannot just charge it for hours randomly. Therefore, you have to know the car battery amps and you can use a battery tester or a digital multimeter to measure it.
If you are using a multimeter, you can measure the volt of the battery. To measure amps, you have to know the ohm rating of the battery. Using Ohm’s law, you can find amps by dividing the measured volt by the ohm rating of the car battery.
However, by doing some back-calculation of a standard car battery, you can understand how much the current charge of the car battery is. You need to measure the voltage by turning your multimeter to DC and putting the red lead to the positive battery terminal and the black lead to the negative terminal.
| Multimeter Reading(Volt) | Percentage of Charge Remaining |
| 12.6 | 100% |
| 12.4 | 75% |
| 12.2 | 50% |
| 12.0 | 25% |
| 11.9 and below | Dead |
When you know the percentage of charge remaining, you can calculate current car battery amps. If a 1000-amp battery has 50% capacity, then the current car battery amps is 500.
Conclusion
Before you charge a car battery, there are a few things you should be aware of so that you can ensure that the car battery does not get overcharged and damaged. We have explained all the important specifications and parameters and illustrated how to calculate amps and hours needed to charge a battery effectively.
One Response
I found the information about batteries I was looking for. This is an ideal start to study further.
I got down a used car battery to couple with a 650W UPS, intending to use for a longer period.
Here in Sri Lanka we have a 2 1/2 hours power interruption daily.
Like to know about fixing of dead 12V UPS batteries.
Many thanks.