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How to determine how many ampere-hours in the car battery

Motorists in the process of operating their car, may enquire: “how many Amps in a 12-volt car battery?” The question is not quite correct, since in Amperes the current strength is calculated, and the battery at rest does not generate current, so this value will be zero. It is more correct to ask the question “what amperage is the battery capable of delivering at its nominal peak consumption?” since the figure can vary depending on the model and design of the battery.

A car battery has a terminal voltage of 10.5 to 12.7 volts. In this case, the amperage may rise from 0 to 150 amperes – depending on the intensity of power consumption.

The starter outputs an average of 1.5 to 2 kilowatts, so at 12 volts the car battery should deliver at least 125 amps.

What is amperage?

Electric current is the directional movement of charged particles through a conductor.

Accordingly, the amount of current is the amount of electricity that passes through the cross-section of the conductor during a certain period of time.

This is where the main nuance is, because this time for the same amount of electricity may be different. In other words, the same amount of electricity can go through in a second or an hour.

This is the concept of amperage: the higher it is, the more electricity passes through a section in a fixed amount of time. To simplify the concept, here is a textbook definition: “Amperage is the amount of electricity that passes through the cross-section of a conductor in one second.”

Number of Amps in a Charged Car Battery

The capacity of batteries is calculated in Ampere Hours, so the question often arises how many Ampere Hours should be in a car battery? This indicator is very important because depending on the brand of car, it needs a battery with the necessary capacity, otherwise, the power grid of the car will be overloaded or vice versa the charge will be insufficient to start and work correctly all electrical appliances. These specifications are set at the factory.

Most often, a 12-volt battery has a standard capacity of 60 Ah, so the peak value when working will not exceed 6 Amps under ideal conditions.

How do I charge my car battery?

There are two ways to charge the battery. The first of them is relevant if the battery is in good condition and the car can start. To charge the battery you do not need to remove the battery, just drive the engine at high speed for 10-15 minutes.

The main thing is to observe two rules:

  1. Do not do it in an enclosed space (such as a garage or repair box), or you will suffocate from exhaust fumes;
  2. Don’t turn on any lights.

After all these actions, the battery will gain sufficient charge, and will gradually recover if you operate the car for at least several hours in a row. It is preferable to do it during the daytime, so as not to create an increased load on the battery by turning on headlights and interior lights.

For the second way, you need a charger. Follow this procedure:

  • Remove the battery from the engine compartment and place it on a flat surface.
  • Unscrew the battery plugs to allow gas to escape during charging.
  • Cover the holes (loosely) to prevent acid splashing onto the top of the battery. This can be accomplished by simply turning the plugs upside down and placing them in the hole slots.
  • Connect the battery charger to the battery, plus to the plus, and minus to the minus. Plug in the battery and set the incoming current to 1/10th of the battery capacity (e.g. 55 A/h to 5.5 Amps).
  • Leave the battery at rest until all cells begin to actively form gas. On average, a full charge takes 8-10 hours, but this figure is relative and varies with the degree of battery wear, temperature, and other things.
  • After disconnecting do not immediately screw in the plugs, but wait at least 20 minutes to allow the remaining gas to evaporate from the battery.
  • Then install the fuses and put the battery back in the car.

It is also worthwhile to be able to determine the degree of charge of the battery. This can be done with a multimeter. A 100% charge of a car battery gives 12.6-12.7 volts on the battery terminals. If it decreases to 12.5, it means that the charge has “dropped” by 10-15%.

In a regularly operated vehicle, the current generated by the battery is on average 12.2-12.3 volts, and this is normal since the battery is never 100% charged in the vehicle except for those times when it is removed for recharging or replacement.


The battery discharges on its own. This happens if the car has not been operated for a long time.

If you have a new battery, and you put the car “at rest”, then after 12 months it is not certain that you will be able to start it.

With old batteries, this figure is even less – no more than a month.

Therefore, if the car is stored for a long time, you should periodically visit it and warm it up – at least once a month. This will not only save the battery but also prevent the oil in the engine crankcase from starting. After a deep discharge, charging the battery becomes difficult, and in some cases impossible, so if you decide to start the car after a long period of parking, buy a fresh battery.

What are battery amp hours?- Video

Max Welder (rvneeded)

Max Welder (rvneeded)

Max Welder is a mechanic enthusiast. Currently, working at a small company. Experienced in electronics, car tools, and security systems. In his spare time, he writes articles for various blogs.

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